There’s a lot of information out there about the different kinds of colour profiles you will need to use, depending on whether you are going to use your stickers for digital downloads or for physical creation and posting to customers.
Basically, all you need to know for the purposes of this tutorial are the two main ones:
RGB – Fine for digital products
CMYK – Much better quality for printing physical products
I’m going to be showing you how to create stickers, but you will probably need to convert them to CMYK if you want to have them printed. Gimp is an amazing alternative to Photoshop but hasn’t yet got around to adding support for CMYK. There are ways around this, but these are beyond the scope of these tutorials. However, below are some resources you may want to check out:
Note that it is not absolutely necessary to use CMYK for printing, but it is highly recommended for colour quality. Also, you will need to use the highest/best printing settings for your physical stickers.