Take a packets of crayons a enough to cater for your party open them a mix them up, now hide them around the room before your guests arrive.
Divide players into as many teams as you need to balance the groups.
Give each team a list of colours they need to find. Then start the race to find the crayons.
When they come back with all of the colours on their list, give them a picture to colour in.
You can now have a simple colouring activity or you can challenge them to race to see which team can be the first to fill in the whole colouring