I believe the yellow and blue Ate fluids (superblue and typ200) are identical except for the color.
If you mix them, you’ll end up with a lighter-blue color, but it won’t cause any problems.
Question: when you say you have ‘extra’, do you mean ‘unopened’? Because once you open a container of brake fluid, you should use it right away due to the hygroscopic nature of the fluid (it absorbs water from the atmosphere). Even if you keep the container tightly sealed after opening, the clock starts ticking after you break the seal, and it really needs to be used within a short timeframe (I’d avoid using it if it has been open for more than a few weeks).
When I flush my fluid, I make sure to buy 2 liters of fluid. If you don’t open the bottle, it has a very long shelf life, so it’s not a big deal if you end up not needing the additional fluid.
– Rob