Red and green are a classic pair of contrasting colours. Whether you go for the brightest version of the colours (as in the top image) or for a more muted effect (as in the image below.)
I think these two pieces are both beautiful examples of how a simple colour scheme can still have great effect.
Top image: Pohutukawa by Liz Smith.
Bottom image: Pomegranate Roundel by Anna Scott.
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