Here's a few adaptations of the opening post, I read the rest of the thread later:
Primary:
Blue - Water - Healing, Purity
Red - Fire - Destruction, Burning
Yellow - Earth - Defense, Attrition, Possibly Decking
Secondary:
Green - Nature - Growth, Behemoths
Orange - Construct - Permanents, Equipment, Metal
Purple - Sky - Spells, Winged Creatures, Evasion
Luminal:
White - Radiance - Symetrical Effects, Illusions, Dispelling, Light
Black - Shadows - Hiding, Sneak attacks, Death
Brown - ??? - No Idea
Gameplay:
You start your turn by drawing a card, then you can place one of the three base colour 'suppliers' into play.
Secondary colour 'suppliers' may then be formed from these. May or may not be available as standalones.
Grey colour 'suppliers' are also available but not as standard and they have less uses.
Cards require their own colours to play but may have some contribution from non-oposing colours (no combining blue and orange). Not sure if grey is ok here.
White cards may be played with any one colour of suppliers but they must all be the same. Not sure if grey is ok here.
Black cards are payed for by 'erasing' non-grey 'suppliers'. This basically means turning them face down and having them become grey. Opposing colour combinations are still banned.
Brown can be payed for with any combination of anything (alternatively, any secondary) and allows opposing colour combinations.
I'd like to suggest that, in addition to their standard function, cards have a "supply colour" and that, at the start of your turn, before drawing, your top card becomes a 'supplier' of that colour. This adds another nuance to deck building. You can fill your deck with OP spells all you like but if they're all grey 'supply types' then you'll have trouble playing anything.
By the way, I am very much a fan of the idea of actually incorporating the colours and their meanings into this.
