从浅绿色到深红色

您可以基于这些颜色的RGB值实现一个简单的解决方案:

green  in rgb is (0,  255, 0)

yellow in rgb is (255,255, 0)

red    in rgb is (255, 0 , 0)

所以你从绿色开始,增加红色直到你变黄,然后减少绿色直到你变红:

public class Controller implements Initializable {

    //defines the incremental change in color 
    private static final int COLOR_INCREMENT = 30;
    //initial rgb values (green) 
    private int red = 0, green = 255, blue = 0;
    @FXML
    private Button button2;

    @FXML
    private DatePicker datePicker;

    @FXML
    private Label lbColor;

    @Override
    public void initialize(URL location, ResourceBundle resources) {
        button2.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent event) {
                lbColor.setStyle("-fx-background-color:"+ getColorString()+";");
            }

        });
        //Cell factory omitted. Not needed to demonstrate the question nor the answer 
    }

    //increment color by COLOR_INCREMENT to step from green to yellow to red 
    //and return string representation of it 
    //green is rgb is (0, 255, 0)
    //yellow rgb is (255, 255, 0)
    //red in rgb is (255, 0, 0)
    private String getColorString() {

        if((green == 255) && (red < 255)) {
            red = (red + COLOR_INCREMENT) > 255 ?  255 : (red + COLOR_INCREMENT) ;
        }else if( (red == 255) && (green > 0)){
            green = (green - COLOR_INCREMENT) < 0 ?  0 : (green - COLOR_INCREMENT) ;
        }

        StringBuilder sb = new StringBuilder("rgb(");
        sb.append(red).append(",")
        .append(green).append(",")
        .append(blue).append(")");

        return sb.toString();
    }
}

请注意,更改的次数是有限的,并由颜色增量的大小定义。2次(255/颜色增量)后,颜色保持红色。
它可以进一步改进,克服这一限制。它还可以从动态(变化)颜色增量中受益。

编辑 你当然可以用同样的方法来改变 DateCell 颜色:

@Override
public void initialize(URL location, ResourceBundle resources) {

    button2.setOnAction(new EventHandler<ActionEvent>() {
        @Override
        public void handle(ActionEvent event) {
            lbColor.setStyle("-fx-background-color:"+ getColorString()+";");
        }

    });

    javafx.util.Callback<DatePicker, DateCell> set = new javafx.util.Callback<DatePicker, DateCell>() {
        @Override
        public DateCell call(final DatePicker datePicker) {
            return new DateCell() {
                @Override public void updateItem(LocalDate item, boolean empty) {
                    super.updateItem(item, empty);
                    //if today, change text and style
                    if (item.equals(LocalDate.now())) {
                        setText(date +"/" + clicksCounter);
                        setStyle("-fx-background-color: "+ getColorString () +"; ");
                    }
                }
            };
        }
    };
    datePicker.setDayCellFactory(set);
}

注意呼叫 getColorString () 两次(一次由按钮处理程序执行,一次由单元格工厂执行)会导致颜色更改两次。
为了防止它,你可以设置一个颜色字段。该字段由按钮处理程序更新,并由 Label 以及电池工厂:

public class Controller implements Initializable {

    protected static final int COLOR_INCREMENT = 30;

    @FXML
    private Button button2;

    @FXML
    private DatePicker datePicker;

    @FXML
    private Label lbColor;

    private int red = 0, green = 255, blue = 0;
    private String colorAsString; //string representation of rgb color 
    private int clicksCounter = 0;
    private String date = String.valueOf(LocalDate.now().getDayOfMonth());

    @Override
    public void initialize(URL location, ResourceBundle resources) {

        button2.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent event) {
                colorAsString = getColorString();
                lbColor.setStyle("-fx-background-color:"+ colorAsString +";");
            }
        });

        javafx.util.Callback<DatePicker, DateCell> set = new javafx.util.Callback<DatePicker, DateCell>() {
            @Override
            public DateCell call(final DatePicker datePicker) {
                return new DateCell() {
                    @Override public void updateItem(LocalDate item, boolean empty) {
                        super.updateItem(item, empty);
                        //if today, change text and style
                        if (item.equals(LocalDate.now())) {
                            setText(date +"/" + clicksCounter);
                            setStyle("-fx-background-color: "+ colorAsString +"; ");
                        }
                    }
                };
            }
        };
        datePicker.setDayCellFactory(set);
    }

    //increment color by COLOR_INCREMENT to step from green to yellow to red
    //and return string representation of it
    //green is rgb is (0, 255, 0)
    //yellow rgb is (255, 255, 0)
    //red in rgb is (255, 0, 0)
    private String getColorString() {

        if((green == 255) && (red < 255)) {
            red = (red + COLOR_INCREMENT) > 255 ?  255 : (red + COLOR_INCREMENT) ;
        }else if( (red == 255) && (green > 0)){
            green = (green - COLOR_INCREMENT) < 0 ?  0 : (green - COLOR_INCREMENT) ;
        }

        StringBuilder sb = new StringBuilder("rgb(");
        sb.append(red).append(",")
        .append(green).append(",")
        .append(blue).append(")");

        return sb.toString();
    }
}

Color 实现 Interpolatable<Color> 接口,以便api可以为您进行插值。

public class Controller implements Initializable {
    private static final Color GREEN = Color.web("#04b404");
    private static final Color YELLOW = Color.web("#ffff13");
    private static final Color RED = Color.web("#df0101");

    private static final double INCREMENT_STEP = 0.3d; // Adjust this

    private final DoubleProperty step = new SimpleDoubleProperty();
    private final ObjectBinding<Color> backgroundColor;

    public Controller {
        backgroundColor = Bindings.createObjectBinding(() -> {
            final double value = step.get() % 3.0; // We get modulus so that 0 <= value < 3

            switch((int) value) { // We will round down the value
                case 0:
                    return GREEN.interpolate(YELLOW, value % 1.0); // Get an interpolate value of 0.0-1.0
                case 1:
                    return YELLOW.interpolate(RED, value % 1.0);
                case 2:
                    return RED.interpolate(GREEN, value % 1.0);
                default:
                    return null; // Shouldn't happen at all
            }
        }, step);
    }

    @Override
    public void initialize(URL location, ResourceBundle resources) {
        button2.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent event) {
                step.set(step.get() + INCREMENT_STEP);
            }
        });

        javafx.util.Callback<DatePicker, DateCell> set = new javafx.util.Callback<DatePicker, DateCell>() {
            @Override
            public DateCell call(final DatePicker datePicker) {
                return new DateCell() {
                    @Override public void updateItem(LocalDate item, boolean empty) {
                        super.updateItem(item, empty);
                        //if today, change text and style
                        if (item.equals(LocalDate.now())) {
                            setText(date +"/" + clicksCounter); // Not sure if you still need the click count
                            backgroundProperty().bind(Bindings.when(
                                    backgroundColor.isNotNull())
                                .then(Bindings.createObjectBinding(() -> 
                                    new Background(new BackgroundFill(
                                        backgroundColor.get(),
                                        CornerRadii.EMPTY,
                                        Insets.EMPTY
                                    )), backgroundColor)
                                ).otherwise(Background.EMPTY)
                            );
                        }
                    }
                };
            }
        };
        datePicker.setDayCellFactory(set);
    }
}