gel coat alone is fine. You can buy a small can that will cure without sealing for little cash.
I would not introduce any other materials as the colour difference will almost always show through on fairing.
Wash with warm water and a brush.
You will need to mix about four times and apply to get depth.
This will give you a chance to match colour.
White gel coat with tiny amounts of yellow introduced will do it.
Yellow can be normal boat paint or house paint as amount is very minimal.
So, you have to mix at least once to understand how much catalyst to mix.
Should end up invisable to naked eye.