GIMP :: Adapting Image To New Background

I have a set of window buttons in XPM format whose background I would like to convert to a blueish tone from their current gray. The problem I'm having is that after blending the button images to the intended blue tone they just don't look good at all.

To illustrate my point, here's the original (menu) button with gray background. Size is 12x18.

Then I took the following steps to try to apply the blue background:

- Manually edited the original XPM and removed the background (it's referenced by the '@' char.)
- Opened it in Gimp and created a new layer.
- Moved the new layer down so it acts as the background.
- Applied a fill to background layer using intended blue color (#2d6fb5).
- Set opacity of layer containing the button to 85.
- In Colours->Hue Saturation set Lightness of layer to 100 so it blends better.

This is the result of the above steps:

As you can tell the result doesn't look good at all. Is there any technique I could use to make the buttons blend in to a more visually pleasing way with the blue tone I chose?

PS: Attached original XPM.