I have a bump on the inside of my cheek thats a bit swollen and a bit discoloured brown/green and red otherwise. It doesn't hurt - what is it?

Listen . it could be trauma, infection, benign or worrisome growth. I would suggest a doctor takes a look....maybe a sample (biopsy) of not resolving soon.
Possible duct. It could be an opening of a salivary gland duct that enters your mouth. Have your physician or an otolaryngologist examine it if the swelling persists.
Picture of lesion. Visualization of lesion and medical history and physical exam required for diagnosis. Any possibility of inadvertently having bitten your cheek?