[cairo] Question about draw colors on transparent gtk window

[Magicloud Magiclouds]

Dear all,
    I want to draw 8 lines of cpu usage on a transparent window on
desktop with 8 colors.
    The attachment is my c code. In line 27, I choose the color of the
line with variable "i". If I fix the rgb values, like "1, 0, 0", then it
draws lines in red. While I use dynamic colors, it only draws in white.
    Why does this happen? Thanks.