1) Go into idraw
2) Go to View
3) Make sure Palette is checked
4) Make sure Tool Box is checked
5) If any of the above are not checked, check them
6) In your toolbox, click pretty much anything. Let's say, the square tool (six down, right column)
7) Right click the background color of the chipset, the one you don't want to appear.
8) You'll now notice the palette has put a box around the color you just right clicked on. Right click that box in your palette. It is now set as the secondary color.
9) Save in iDraw, and open RM2K
10) Go to Tools>Resource Manager
11) In the left hand column, select Charset (6th one down)
12) Click Import towards the right.
13) Find your file and open it
14) A new window will pop up. Click the background color (green?), and it'll start flashing. This is the part that will be removed as transparency when you play your game. Hit OK.
15) Play your game! When selecting event/hero graphics in Event Editor or the Hero Database tab, you'll still see the background color, but when you play you shouldn't see it, leaving just your character!
Did it work?