Syntax definition for 6502 assembler for Sublime Text 3.
Ideally, you would install this syntax definition through package control: Preferences/Package Control/Install Package/6502asm-sublime. However, the current version of this package is not on package control yet. Work in progress.
Alternatively, you can download this repository and copy the contents into a folder called 6502asm-sublime in your Sublime packages directory.
You will probably need to restart Sublime.