color map with specific range

I have a scatter as shown in the fifure below. i want to do is if y value biger than 1 has a red color and above 3 is yellow and above 4 is red. how can i do it . thanks in advance

Answer 1

[Star Strider]

I used 'filled' here because otherwise the yellow points may be difficult to see —

figure
imshow(imread('tri.jpg'))

x = 1:85;
y = 6*rand(size(x));

th = [1 3 4 max(y(:))];
c = 'ryr';

figure
hold on
scatter(x, y, 25, 'b', 'filled')
for k = 1:numel(c)
    Lv = y > th(k) & y <= th(k+1);
    scatter(x(Lv), y(Lv), 25, c(k), 'filled')
end
hold off

.