In your plot calls, use the LineSpec argument (see this) or 'Color',c input argument pair (see this).
Examples:
figure
hold on
plot(1:10,'r') % red color, using LineSpec with color short-name
plot(2:11,'Color','k') % black color, using 'Color',c property/value pair with color short-name
plot(3:12,'Color',[0 1 0]) % green color, using 'Color',c property/value pair with RGB notation specifying the color
More examples:
figure
hold on
plot(1:10,'-s','Color',[1 0.5 0]) % solid orange line with square marker
% orange has no short-name, so it can't be included in LineSpec;
% you must use 'Color',c property/value pair for specifying this color
plot(2:11,'--r') % dashed red line
plot(3:12,'-gd') % solid green line with diamond marker
