if u shoot in raw format... and if u are using canon camera... u can open up this raw format photo in DPP (Digital Photo Professional) supplied together with your camera... then u can apply a S curve on this photo to enhance the colors.
for Canon, adjust your picture style
for Nikon, adjust your picture control setting.
The settings will be applied to all JPG and RAW(only if openned by their respective converters, DPP / NX2)
For RAW if you use other converters like Lightroom, Aperture, Adobe Photoshop, the picture style / picture control settings will not be applied. thus you have to adjust your colors during PP
I have been wondering about this as well. The colours on some models really pop whereas others don't. Is it the lens, or the body?
The other thing I've realised is that when shooting in Bulb mode, the colours seem alot more vibrant. This of course can be solved by changing the colour saturation to "vivid" as mentioned by previous posters. But what if you just want deeper colours that don't necessarily go off the vivid scale?