A couple of things, Yellow ackies can have red and still be yellow ackes. The name reflects their subspecies. Yellows are V.a.brachyurus. Red ackies are, V.a.acanthurus.
For instance, Red ackes can be brown or orange. But they are rarely yellowish.
Yellow ackies can be tan, yellowish, have white down the back, have striped necks. They also have smaller spines on the tail. They also seem to be of lighter bone structure. Smaller heads, and they do have way smaller eggs, as much as half the size of red ackie eggs.
Both can get over two feet. I have seen a yellow that was three feet. I raised a yellow male to 27 inches in one year.
Red ackies seem bigger, but the longest I have seen is about 30 inches. But do grow to two foot or over very easily in captivity.
Post pics of your ackies, then we can see if they are crosses. Also, about 7 years ago or so, some german reds were imported. They are a reddest form of Yellows. They come from the same area. Cheers