What are the 3 colours that looks good for some combination in a monochrome painting?

I have to paint using 3 colours for a monochrome painting. From each of the 3 colours, I have to use 4 either shades or tints colours so in total I have 12 colours to use. My drawing contains nature influences in it, and some rather complicated shapes in it, so I'm really confused in terms of choosing the colours >.< Think you can help me? >.<

What is a VPN?

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