For those Canon folks that shoot RAW, the Canon Digital Photo Professional (DPP) software has done the most accurate color renditions, particularly the red channel and to some extent in yellow. DPP has improved in terms of workflow, but PhotoShop (Adobe Camera Raw + PS) is commonly used by many photogs, myself included. Working around the differences in red & yellow conversion in ACR is a bit bothersome. Adobe Labs released a beta version of camera profiles in July for Canon that improve the accuracy of the conversion.
These shots are straight out of the camera, no adjusting or processing.
ACR without the beta camera profile
ACR with the beta camera profile. Note - this what the colors should look like
The red in the above examples is extreme, but it illustrates how large the difference is. Naturally any color that contains red, and to a lesser extent yellow, is effected.
There is also a beta DNG editor for those that want to edit/create their own camera profile. The camera profiles only work in ACR 4.5 or later, and only in Lightroom 2.0.
http://labs.adobe.com/wiki/index.php/DNG_Profiles