Not possible in the literal context you described. Individual character formatting cannot be applied to values in cells that are returned by formulas within such cells that contain formulas. This is because formatting is applied to a specific character location, and such locations vary depending on the result of the formula. There is no way for Excel to know in advance how to format a result it doesn't know yet.
The only workaround is an event that basically enters the formula, converts it to a value constant, and formats the characters of that constant based on criteria you predetermine. Even then, no formula would actually exist in the cell except for a split second, during which time no formatting exists. The end result is possible with some imaginative coding of what are essentially constant cells.