Archaeplastidia

You eat a photosynthesising bacterium.  It’s tasty food.  However, over time, you have found that allowing the photosynthesising bacteria to live for a little while inside you makes them even better, as they can continue photosynthesising and making sugars inside you.

In fact, you have evolved to provide the chemicals the photosynthesising bacteria needs as food to extends its life inside you and maximise your meal

This adaptation has now reached the point where you can contain multiple photosynthesising bacteria and they can live on inside you indefinitely.

You have entered a symbiotic relationship, and will come to rely on your guest, providing food and protection, for the price of a few sugars.

Your guest photosynthesises using a chemical called 'chlorophyll a', which turns you a blue-green colour and gives you a supply of sugars all the time you are in sunlight.  It doesn't absorb all the sunlight though - only a part - the rest is wasted.

The usual copy-error effect - inside the guest living inside you - can give you the ability to make a slightly different version of chlorophyll which will work using a different part of the sunlight spectrum, but it means you'll make less of chlorophyll a.  Interested?

I'll go with two.
The one I have is just fine.