I am still trying to contact AtariAge's maintainer just to get Javatari added to the list of Atari 2600 emulators. I did it many times, but never got I single reply.
I really feel just ignored sometimes... but maybe its the language barrier.
Albert is a nice guy, he aways busy making homebrew carts and keeping the site / store. It's not your fault, the AtariAge database also needs to be updated (See here) just too much things to do.
I used to play with Zsnes until Stella was vastly improved and become my favorite emulator, manly because the debug (I'm a 2600 programmers and it really helps). Keep working on your emulator.
I was testing sloped girders changing the color on the fly. It's possible only on half of the screen, There is no time to change assimetrical playfield plus bg color change on the fly (mirrored PF require changes for PF2 exactly at @48). Also no time for players and others stuff, sadly. I'll post here anyway, just for curiosity.
The PF are masking BG colors changes, don't know why I did this way, it's same effect for change PF colors. I still have some ideas but very much will not work.