well since you only used 2 collors for the fase, you could do transparant background for the rest of the image and you have 2 colors.. Also you can add 3 kinds of blue, and create kinda the same background with some dithering, but than you have 5 colors total..
It's actually 13 colors. I recounted. There is a layer of low opacity white over some parts of the hard which changes all the plaid colors in the background.
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