I don't know if the flame color would be an issue, but an odor would be of more concern to me.

You can get a CO detector to make sure it's safe:
http://www.pksafety.com/uei-carbon-monoxide-detector-co71a.html?gclid=CKPBhK_qi8cCFVOQHwodT8YLVw

We just installed a new oven a month ago and noticed that although it uses natural gas, it gives off an odor when both top range and bottom oven are turned on. It's that usual smell burners give off, I think, but it's strange even the bottom smells too, right? Also, while the top burners are blue, the bottom oven fire is orange. Anyone know if this is normal? It's a new oven and was tested by installers. Seemed ok then.