Since your colors are really just numeric values, we can perform an interpolation on those numbers using interp1:
b = [0 0 1]; % Blue
r = [1 0 0]; % Red
x = 0:0.01:1; % Values to interpolate on (This would be your actual vector of values)
xOk = [min(x);max(x)];
% Interpolate over all of the values in x
y = interp1(xOk,[b;r],x); % Here Blue corresponds to xOk == 0 and Red to xOk == 1
scatter(x,x,[],y) % Scatter x vs. x but color based on the interpolated color.
