There are three species of albino plec:
1. The albino bristlenose, like this:
Females will develop some very stubby bristles at the very most, pic is of a male (Ned Flounders). These grow to about 5". Can be very pale pink or slightly yellower (the yellower ones often being sold as "Gold Bristlenose").
2. The "albino common plec" - a dirty looking albino form of the common plec, Liposarcus pardalis. Sometimes sold as "chocolate albino plec", or "chocolate plec" (although there is another species which is the true Chocolate Plec).
Pics are of a juvenile (Hannibal Plector) - they are often a little bit paler and get paler as they grow too, to a greyish, greenish pink. These grow to roughly the same size as a normal coloured common plec, so a good 15", maybe a little more.
3. The albino gibby/sailfin, Glyptoperichthys gibbiceps:
Image nicked off Google, sorry it was the best I could find. These grow to similar sizes to their normal coloured variant, so 18"+.