You have an Atwood water heater
Your Flame is burning Fuel Rich...not enough air
Clean burner/orifice/burner tube
**Disassemble burner tube (clean with small bottle brush), remove orifice (soak in alcohol the air dry----NO high pressure air or poking anything thru it), combustion/exhaust tube (run wire thru then tie rag to end of wire and pull back thru...chimney sweep)
Reassemble.....fire up water heater
Adjust 'air shutter' so flame is BLUE with slight roar