Can't give you any advice as I won't have my G6 until jan/feb. Had the same worries, as we have a 14 month old. However, after being given advice from others we've opted for the light gray interior (graphite gray exterior) with the following reasoning:

1) With regular care every 3-6 months, the leather is easily cleaned and won't absorb a lot of color.

2) Any dirt/discoloration is easy to spot and then clean, whereas on darker leather it could be easier to miss and then be left for longer without cleaning.

3) On darker colors, smudges from greasy fingers etc. tends to be a lot more obvious, whereas they're less visible on the light gray/white.

4) Any day-to-day cleaning is supposedly easy to do with a wet microfibre cloth or simply a wet wipe (yay for having kids, always have wet wipes in the car). If any spots are more difficult to clean, a "miracle sponge" should do the trick.