colourful image labeling by using plot function to generate a scatter plot

I have two vectors with 1000 length each. for example

r1 = rand(1000,1);
r2 = rand(1000,1);

then I want to plot a scatter which shows r1 versus r2 as follows:

plot(r1, r2, 'or')

I want to show each two values of r1 and 2 with the same color but different from the rest. any suggestion ?

I wrote something but it does not fully help me

for i=1:size(r1,1)
plot(r1 (i,1),r2 (i,2),'o')
hold all
end

Answer 1

[Mike Garrity]

The scatter command lets you assign a color to each marker using the CData property:

h = scatter(r1,r2,'or')
set(h,'CData',1:1000)

Is that what you're looking for?

[Niki]

Not really, as I explained above, I want to plot for example the first two values in blue, then then second two values in green etc. In general, each two of those scatter will have the same color.

Answer 2

[Mike Garrity]

I'm not quite sure I follow, but if your CData array looks like:

[1, 1, 2, 2, 3, 3, ...]

then every pair of markers will be the same color.

For example:

c = 1:500;  % go through colormap in order
c = repmat(c,2,1);
set(h,'CData',c(:));

or

c = randi(64,1,500); % 64 random colors
c = repmat(c,2,1);
set(h,'CData',c(:));