A little off topic, but does the Reserve grid being red have anything to do with allowing trip swaps/drops?

For example, Xmas eve was +1 in the green before 0900 today, tried to drop a RES day within 5 seconds of the 0900 FCFS start time, no dice, I guess too slow as it denied due to coverage at or below mins. After that, I couldn't drop a RES day for that day since it was no longer green, but watched it drop all the way to -4 in the red with more open time being added on that day. Couldn't find anything in the FSM that gave specific guidance. I assume if you're a line holder you can drop trips with the Grid in the red? Thanks.