I would suggest using a rule to set Attribute Value Visibility to visible/invisible depending on the value of your paint type. For example:
I have an asset with two attributes: Paint and Subitem.
Like your example, I only want Subitem to show #paint-a-sub items in the dropdown when A is selected and #paint-b-sub when B is selected.
By creating conditional Attribute Value Visibility rules like this:
Your dropdowns should be populated correctly:
Gif recording here
Let me know if this is a suitable approach.