We don't normally do the gloss wave in Breeze. That's more of a Tango/Oxygen thing. How about adding some holes instead to make it look more like the real thing? https://www.gamesworld.com.au/wp-content/uploads/2015/10/cardinal-four-in-a-row.jpg

Just some ideas: Use light gray or white circles for the holes and black and red for the pieces (like in the actual program). Take a look at the kiriki icon. The way it does indentations can be inspiration for the holes.

I think the icon is lacking gradients, especially the shadows, which are always supposed to be linear gradients.

Also please add a one-pixel hard bottom shadow.

I just tried the patch on my own computer and I noticed a few more things that need to be changed:

• The canvas size is 128x128 px when it should be 48x48
• Strokes need to be converted to paths ( Ctrl+Alt+c ). Strokes don't always look correct in various SVG renderers, including the Qt renderer.
• I see you added a shadow inside the darker blue rim, but while you can do that, there also needs to be a 1px high shadow on the very bottom for it to match the HIG.
  • There are some exceptions, but they are not common (or the icon creator and reviewers just forgot ¯\_(ツ)_/¯ ).
• The top left and bottom right corners are not aligned to the grid:

Suggestions regarding the colors:

• I think the icon would be more recognizable if the board had a darker color instead of a lighter color. The board itself could use a gradient, but I assume you're still planning to add that.
• For the indentations, I think they would look more natural if their colors were based on the board's colors rather than the pieces' colors.