What exactly do you mean by "on a scale"?
If what you're looking for is a means to have the line colors share a continuous colormap, then you can do that by setting the 'colororder' property of the parent axes.
N = 14; % number of lines in plot
% test data
x = linspace(0,1,100);
g = [1:N/2 1./(1:N/2)].';
y = x.^g;
% plot it
plot(x,y,'linewidth',2);
% pick some colormap and apply it to the colororder property
mycolortable = parula(N);
set(gca,'colororder',mycolortable)
