A colour theme for bride, groom, bridesmaids, best man and ushers is fine, but for guests? I'd be a bit
if I was told what colour to wear. Dress code is also fine, so you know how formal/informal the wedding is.
I saw some wedding guests recently (having a pre-wedding drink in my local pub). The theme must have been deep pink or gold, because the majority of the women were dressed in those colours, with their OHs in matching ties. But there was one woman there who either didn't like, or wasn't prepared to buy, pink or gold. She was wearing a gorgeous dark green dress - I thought "good for you" 