The "yellow/gold" (orange) color sounds like the standard icon for a USB or FireWire volume. When you assign it as your Time Machine volume, the icon becomes green with a symbol of a counter-clock-wise arrow around a clock.
As long as your are starting up from your normal startup volume, it should be green because that system uses it for Time Machine. If you start up from another volume, it is probably the orange color, because to that system, it is just a regular USB or FireWire volume.
Does the color mean anything regarding the state of the backup?
No.
When do you notice that it is orange?