Can anyone help me tweak the colors of the grills in Mars Station to better fit with the greys of Celestus Pravatis?

I'm looking to put some grills on the outside of a Clelestus Pravatis spaceship build (see this thread).

There are some superb grills in Mars Station, but the colors and grunge levels are so different to Celestus Pravatis that they will look out of place as they are. Tweaking the colors of the Mars Station grills to align with metallic greys of Celestus Pravatis should solve this problem. Only difficulty is, I don't know how to do this (and only have the GIMP, but no experience, to use for this).
Can anyone help?

Anyone? Any pointers to how to do this with the GIMP?

Hmm... I know how to do this with Photoshop, but not GIMP...
Anyone have any GIMP experience? Help a brother out.

Mind you I am no expert in GIMP, but I have played with it a bit.
Lets see...
Try the colors menu specifically Color Balance, Hue Saturation (for adding Grey and darkening or lightening), and Colorize for changing the color of the image. If you are just changing the color of a specific spot then use the lasso tool to isolate the area and then cut it out and paste it into a new layer.

If that doesn't help then just google some tutorials to get through the basics. Like I said I barely know GIMP as I am more familiar with photoshop.

Yeah isolating the bits you want to recolor is key.

Also when you like the look of the preview, always write down the settings for it. This is VERY IMPORTANT.

Also sequential adjustments can be done. When I did my fall trees I had to first change the green leaves to yellow and then from yellow to brown. It wouldn't go straight from green to brown no matter how much I tweaked it.

Every time I recolor stuff its just a LOT of playing with the settings until you get something that looks right.

Thanks guys - looks like its time I got to grips with the GIMP.
I'll have a hunt around for beginner tutorials - if you have any recommendations for good ones, please let me know.