[intel352]

is each size/color a different sku?

Product Options works as Groups of options. Those options can be a Text Box (text entry by customer), Modifier (just a dropdown per group for color, size, whatever you enter, that can change price or have no effect on price), and Variant (manages it's own stock level, has own sku, own image, etc)

You can add multiple Product Option groups. If you add a variant group of Colors, and a variant group of Sizes, X-Cart will automatically pair up all of those colors and sizes into 1 Variant per combo

Ex:
Sizes - XS,S,M,L,XL (group specified as Variant)
Colors - Black,White,Blue (group specified as Variant)

Resulting Variants:
Black - XS
Black - S
Black - M
Black - L
Black - XL
White - XS
White - S
... etc etc


And that will track qtys & sku for each combo in the admin. The customer will see only 1 dropdown, showing "Black - XS", etc.

Alternatively, if you only need to track Color qty, but not Size necessarily:

Ex:
Sizes - XS,S,M,L,XL (group specified as Modifier)
Colors - Black,White,Blue (group specified as Variant)

Then your variants in the admin would only be the Colors group. The customer would see 2 dropdowns, one for Colors, one for Sizes, and any purchases would only affect Color's inventory of course.