Normal wear and tear probably! Contact dermatitis I would say. Make sure you are using a lube you tolerate well.
Things to think about regarding bumps: are you sexually active, do they itch or cause discomfort (other than after masturbating), are they changing over time.
Light purple color totally normal.
i am sexually active, the bumps don’t cause discomfort and don’t really feel or look like bumps. thank you
Are you washing your penis with soap and shower gel? - you should only use water, and dry throughly.
Do you use a lube for masturbation and sex, and condoms for sex always?
What you need to think about is everything that is in regular contact with your penis that is chemical based, the vast majority of bodily cleansers are, for example. What happens is that your skin eventually develops an intolerance to what it is in regular contact with - the ‘cure’ is to remove ALL chemicals from contacting your penis. Because your are fully circumcised this will make that process harder for you to achieve.
Masturbation and sex can also be a problematical and this heightens the effect of the intolerance as when these are taking place there is a great deal of friction going on for the skin at the top end of the penis. Ease back on the frequency of masturbation would certainly help, abstaining all together for as long as you can will be even better …