What are you talking about @
Luis xd he's using SD, why decompile the .swf using rabcdasm when the SD client source is provided..
Anyways, @ OP take a screenshot of the color you want to change, open the screenshot in paint.net or something, find the hex color, ctrl+shift+f (search) in intellij for that hex color, and it will take you all places that hex color is found, if you want to change the red side bar (in SD client, since that is what you're using) there will be a lot of occurrences found, change them all, only because that red on the side bar is used for multiple things, the side bar, the login panel, register panel, all panels basically, etc. but changing something like the color of name on the side bar it will only be in one place, sometimes the same color can be used for different things in client, look around each file it brings you to to find out what it's used for to make sure you're on the right file with the hex color in it. like if you see something like
playerName.text = player.username; for example and then above it is a hex code in the parameters of the simpletext line, that is obviously the hex color code for the players name on side bar in-game.