As per your description, you either want to set different colors to each line in variable 'hlines' or you want to set multiple colors to a single line (varying colors along Y axis).
1) You can set different colors to each line using the code snippet below.
colorstring = 'kbgry';
for i = 1:5
set(hlines(i), 'Color', colorstring(i))
end
2) As per the link below, it is not possible to set different colors for different region of a line.
However, below link that illustrates the usage of patch objects may help you.