How to draw line with different colours?

[krunalpaliwal]

what i want it when user draw
1st line in white color then choose red color
2nd line drawing in red color then choose green color
3rd line drawing in green color.

I have change in stroke array but when I try to draw with different color all other lines are convert to same pick color. But when I do undo operation I got the old color value.

Any idea how to achieve this thing?

Thanks.