I've almost finished writing a PureBasic application that lets me design single screens/levels for the Commodore64. It's called 'ChillED' and will be used to design levels for a C64 game I'm coding.
The application lets you load, save and edit C64 charsets and then edit screen RAM and colour RAM and then save the whole lot out to use in C64 games.
I'll plonk a link to download here in the next few days once it's undergone final testing. In the meantime, as part of my destruction testing, I ripped a charset from a famous C64 game and recreated the title-screen using my editor. In the screen dump attached, the screen being edited is being displayed using the 'Colodore' palette, with scanline and CRT emulation switched on.