Thanks for your query.Based on the facts that you have posted it appears that you have noticed change in colour of the glans
of your penis after erection
This is normal phenomenon to change the colour due to increased blood flow in penis on erection and it is nothing to be worried abut.
The engorged veins by the side of the glans may be prominent dorsal veins which varies from person to person. There is no danger of getting those veins thrombosed at all and to develop gangrene
of the glans as it has dual blood supply.