If people are asking whether they should spell it colour or color, that's probably the reason they are not doing well! What a ridiculously pointless thing to worry about.
For me there is an elephant in the room regarding UK startups not achieving the same sort of success as they do in the US. It's quite simple. People in the UK are far more risk averse than people in the US. It's a completely cultural thing, and it's not going to change any time soon.