Hi Nigel,
Lots of ways to change colour, but here's one:
To get the olive colour, first select the dial with a circular marquee (using guides & holding the shift key to constrain to a circle helps)
Then use image> adjustments>selective colour
pick greens in the selection box, then play with the sliders to get the shade you want.
(I've used cyan +100, magenta +55, yellow -55, black +55)
Use the neutrals selection to darken the selection (I've used Black +15)
Alternatively you can use image>adjustments> hue/saturation
-move the hue slider to taste.
(note that this changes all hues together, but for this simple single toned image, it should be fine)
Both of these methods can be done as a layer. This allows you to go back & change things as necessary.
As for the silver look. Not sure what you are looking for.
If its simply a brushed steel sort of look, try:
-select dial
-create new layer
-ctrl-backspace to fill
-filter>noise>Add noise
- about 50% gaussian monochromatic
-filter>blur>motion blur
-any direction (I use horizontal) & about 100pixels
-use different blend
modes & opacities to taste.
can also add a metallic higlight:
-select dial
create new layer
-use gradient tool select circular gradient
-drag out a spot from within dial
-use layer opacity & blend
modes to adjust to taste
If you are looking to metallicise the numbers & markings it gets a bit more complicated.
I'll see what I can come up with.
Let me know if I'm not clear enough or if there are any problems.
Cheers
Joolz