Thanks for your query,
The precum is a watery secretion that one gets during fore play It is secretion of mucus by Bulbauretrhal glands due to sexual stimulation It is not contain semen at all.
To much arousal during foreplay is a normal phenomenon and will not cause any damage to penis .
The colour of the glans penis
changes during erection due to increased blood flow and nothing to be worried about .It is normal.