Recently I designed some patterns for china mugs which were going to be screen printed. With screen printing, the more colours you use the more expensive it becomes, so I had to go through the process of reducing colours as well as using the same colours across several designs. When it came to counting the colours in the design, I literally looked at the design and counted the colours, which wasn't an exact science.
It wasn't until recently I realised a handy way to count colours in artwork is by using the 'recolour artwork' tool. You simply select the artwork and then click the 'recolour artwork' button and hey presto, you have the amount of colours shown!
So I thought I'd pass this on in case other people didn't know about it.