No, with gui, color shift effects gray scale, not A scale. The icon just doesn't have transparency.
oh, i just noticed when i looked closely it has a square grey icon, rofl.

EDIT: @lance
Do this;
1. Go to Construct
2. Make a wall of white glowed print bricks
3. Make them blank using the printer
4. Select any of the bricks with the wrench and spawn your weapon in the right direction you could see.
5. Take a screenshot (CTRL+P) on any angle you want it to be
6. Go to photoshop
7. Open the screenshots folder in your Blockland directory and find your weapon screenshot.
8. Open it and go to the layers and double click the background layer, it will turn into Layer 0
9. Go to the magic wand tool and it will cut the color white in the image, just click in the white in your screen shot and press DELETE
10. Now, you've made your screenshot transparent. If don't repeat back to Step 1.
11. Save and open in photoshop the Template.png from this
tut11.1.Go back to your screenshot window
12. Use the move tool (2nd Icon on the toolbox ) in the tools and drag the layer of your screenshot to the Template.png window.
13. Its oversized right? Go to Edit > Transform > Scale
14. Make the Template.png window bigger so you could scale it.
15. Adjust it to the right size, and you can add more effects (depends on you)
16. Save as > PNG file
17. Save it to your Blockland Directory > Addons > ItemIcons.