My father have urinary retention and he's wearing catheter for two months now..blood is seen in and around his underwear also sometimes his urine looks yellow and sometimes look red..what causes this?

What you described warrants evaluation by a doctor, preferably by a urologist. It is not feasible to provide a meaningful opinion without examining your father.

Bleeding from the meatus due to catheter irritation is common for patient with relatively new foley catheter. Episodic bladder bleeding is also common in this case which is the cause of red colored or blood tinted urine. You have to pay attention to the cloudy with foul odor urine when your father seems sick because urinary tract infection may occur. Catheter should be changed monthly if feasible.