The hardest part of a repair to the surface of a coloured fibre glass boat is matching the colour shade. Even "factory colours" don't match exactly after a boat has been in the sun for a few years. The best way to match the colour of your boat is to use a colour match gel coat kit. (Internet search engine tip: Enter colour match gel coat kit + your area).
A colour-sample card from your local paint shop that matches your hull can provide help. Ask the shop assistant the ratio. They custom-mix the colour by adding tints to a white base, the same as in the kits. The formula may call for a half-dozen different tints, but the important ones are those specified in the largest quantities. You can use the tints in the kit to approximate the ratio.
Always colour gel coat before you add the catalyst. Keep track of the number of drops of each tint. When the colour looks close in the cup, touch a drop of the mix onto the hull. Make needed adjustments until you are satisfied with the match then write down the formula so you can duplicate it for the rest of the paste.