One says Stop one says Start and the writing on the button is easier to read than that in the progress bar.
But as I said I’m not actually opposed to change…
For the record, this is the first time I noticed this and only because you mentioned it. I squinted at the screen to confirm you are indeed correct.
Glasses, some of us squint. 
There’s a fine line between visual delimitation and visual subtlety. It should be crossed in favour of delimitation, when possible, IMHO.
What I mean by this is that, for me at least, it’s easier to recognize differences in colours than it is in letters.
At the same time, I don’t want to beat Renoise with an ugly stick.
Compromises are difficult.
Clearly, the general feeling seems to be that we need something a bit more than a simple text change, since this may not be completely obvious to users viewing it at a glance.
So, keeping in mind the custom theme colours the user may have, how does this look?
2485 
Or even this?
2486 
OSX: Growl popup, Renoise icon also starts jumping in Dock when rendering complete 
dBlue that white for complete looks good. Red for fail? (ran out of diskspace?)
This is possibly my favourite suggestion so far. Expect bear in mind (as dBlue has brought up) that the Themes in Renoise are 100% customisable, so saying “go from yellow to green” is a little bit worthless. I have to admit that I often find it hard to work out which colours in the Themes section are actually used where and I’m not sure a fully new colour entry should be used for this… Would an RGB inversion or 180deg phase change of Hue on completion possibly work OK without further complicating the Themes?
It could definitely be nice to have red for failure, green for success, etc., but this means adding more crap to the theme system. In the end it’s a lot simpler to re-use existing colours in the theme, and then we can easily respect whatever the user prefers.
If I had my way, Renoise would only come with maybe 3 hard-coded themes at most; one with a white-ish background, one with a black-ish background, and one with a grey-ish background. Each one would then be specially designed to look amazing at all times, and we could use all kinds of great highlight colours that were guaranteed to always fit the theme and be correct. Probably a good thing that I don’t have my way, though, since the community definitely seems to love their bizarre colours, haha.
It’s a color change. drastic enough to get the point across clearer than it is w/o relying on yet more theme options.
If i look over and the bar is yellow, it’s still rendering… if i look over and i see it’s gone grey with yellow text I know it’s done.
edit for further clarity: (replace yellow with whatever your fav theme’s highlight color is)
i must admit i know the ‘issue’ mSepsis is talking about here. when i first rendered something in Renoise, my very first reaction was to hit the ‘Start’ button again. i really had to look twice to see that it had stopped rendering (and i don’t wear glasses).
i think dblue’s suggestion is the best one made so far. a simple color-change would be a pretty clear and obvious way of showing something changed. i think it would indeed be important to stay ‘in-theme’.
i would appreciate a dialogue window with “ok” (ok would exit out of the render dialog and back into the tracker) “show file” (open OS explorer/finder to folder) and “back to render dialog” (back to render dialog)
bump n grind
for the record seems in the latest 2.8 beta the theme assignments have changed… now my render bar color is the same as the font that goes over the render bar, so this:
actually is saying the render is complete… but you wouldn’t know it.
I’m hoping this proposed progress bar color change proposal makes it for this new release… It’s such a minor tweak.
since we’re talking about this thing I noticed the percentage is invisible before around 50% because the colour of the text is the same as the background.
How about 3rd colour for the text or background.