Combining string to hexadecimal and maybe vice-versa

Hello, I have a LCD display that requires hexadecimal rgb values.

String rgb = 000000;

I need to individually increase lets say red, and then convert the final product into a full 16-bit hexadecimal color value. So I'm thinking I need to read the first two characters, convert them to hexadecimal values, increase them, convert back to strings, and re-insert into the main string.

Then, each time I want to use the string, I convert it into a hex number and use it.

Getting the induvidual digits and combining them and re-inserting is easy. Strings are mutable in C++ (I think... I'm new to C++). But I do not know for the life of me how to convert from string to hex and hex to string.

I appreciate the help!

Try this,