I sent an email to Dexcom Tech Support which I copied below.
I have had my G4 system for almost 3 months now and totally love nearly every design element. Except for the RED numbers for lows. While I appreciate the urgency of a hypoglycemic event, when my blood sugar is low, my brain is already working less than optimally and the red numbers on the display make it that much more difficult to read. I’m not exactly sure who decided on this particular feature but he/ she obviously has never experienced a low of any kind or he/she would have made the low numbers as easy to read as the normal and high numbers. I would really appreciate it if the display numbers could continue to be white or yellow and the dots beneath the “low” line are red.
I don't know if anyone else finds the red numbers hard to read or if it is just me. They did get back to me and thanked me for my input. They'll pass along the information to their Marketing Team. I'm pretty sure, there is no way they will change my receiver so I can actually see the numbers when I am low, but maybe they will change them in the future.