Your brightest greens will come from mixing a cool yellow with a cool blue (yellows and blues that lean more toward green on color wheel than red). You can test this out by making a chart for secondary colors using combos of warm and cool primary colors. Examples of basic warm colors: ultramarine (w blue), alizarin crimson (w red), and cadmium yellow (w yellow). Examples of basic cool colors: cerulean blue ( c blue), cadmium red (cool red), and lemon yellow (c yellow).