Pink Grapefruit

BJ11 says...
The pink in your grapefruit comes from lycopene, and if you're not getting pink then perhaps your plant is not synthesizing enough. (The plant also has carotene - but I'm going to presume it is the 'pinkish' you're losing and not the 'orangish').

Why it is not synthesizing enough lycopene is the key to the problem. Either it doesn't have the ingredients (unlikely as it is still healthy), or it isn't synthesising enough).

Synthesis begins with mevalonic acid.
I hope you're not peeing on the plant after taking cholesterol lowering medication are you? (Or loads of other medication - non-medicated pee is good!). Some chemical inputs will impact on this chemical.

Mevalonic acid is then converted and glued on to a few other compounds in several steps, so you'll want the right bugs and fungi in your soil to help with that. When in doubt - add lots of happy, healthy compost. Synthetic fertiliser will not help here - you need bacteria or a highly sophisticated lab to glue the right chemical together in the right way.

The plant then finishes the job to converted into lycopene - pink grapefruit.

Perth weather has been weird - this can also be disrupting little buggies doing their thing. Too much rain might be washing nutrients through the sand quickly.

Try critter-rich compost, leaf mould, and non-medicated pee.