This is a duplicate of Syntax colouring when using Symbolize, but that post is almost eight years old and hasn't been active in almost four years.
Is it possible to get normal syntax highlighting for variable names made with Notation`Symbolize
? E.g.
<< Notation`
Symbolize[ParsedBoxWrapper[SubscriptBox["_", "_"]]];
Subscript[a, h] = 2
Solve[{
b == Subscript[a, h],
Subscript[b, k] == b}, {b, Subscript[b, k]}]
Produces the following, where subscripted variables have been highlighted either wrongly or not at all: