Synthetic Oil

[07WYarisRS]

Don't worry about the color of the oil.
Most color is caused by particles in the oil too fine for the regular style filters to trap. If you were to use an Amsoil by pass filter and the 2 micron oil filter set up you oil would still look good even after 100,000 miles.
Synthetic will tend to get dirty faster on enegine that were run on dino oils as they clean away deposits that have built up over time and prevent new deposit build ups.
That's why the sooner you can switch the better.

As for the royal purple VS amsoil question
Both are decent oils, However I have personally seen the lab results from a couple of royal purple tests and they showed serious issues with their quality control. In one case the oil grade on the bottle was higher then the actual oil in the bottle. I've also seen high levels of copper and water.
Amsoil and Redline IMO are two of the best lubricants out there.

Asfor the roatary engines, That does hold some truth
But I would not worry about running Amsoil in An RX7 or -8.
Poorly refined caster oils (bean oils) do form heavy gummy deposits when exposed to flame and severe heat and this will build up over time.
Amsoil or redline oils do not form any such depostis.
I have seen some of my engines with hundreds of hours on them and ZERO carbon, ZERO build up anywhere on the combustion chambers or pistons.