From my uninformed POV, ACR, compared to other programs such as DPP, don't exactly get their colours spot on. My 350D, when using ACR, is reasonably hopeless with colours, in particular, the red.
To fix this, you can shoot a colour chart (such as a Gretag Macbeth) and then use a freely available script to analyse the image and provide you with the correct adjustments to feed into ACR/LR.
Now, purists will say that every camera is different and you must shoot the chart yourself and then analyse the image. I say, that something is better than nothing and since tweaking my ACR, my colours and clarity are improved. Reds are a thousand times better.
And, for the 350D users, here is my user preset for LR and a 'Daylight' colour cast (but I find it improves most images, no matter the WB):
Red Primary
Hue: -12
Sat: +28
Green Primary
-27
-21
Blue Primary
-3
+2
Edit: Tweaked my interest and did some more research, 350D Daylight (5000K) values have changed.