1- You cannot change menu or guide colors on 508D
2-If your recording is not "limited" you can keep it forever. If your recording came with expiration date, your recording will dissapear after that date or withing 24 hours after you watch it.
This is from Dish website:
Limited recording restricts the amount of time that some Pay-Per-View movies can be kept on your DVR. If a Pay-Per-View movie has “limited recording” (which appears in the first order pop-up screen), you can record the movie to your DVR and will have until a specified date to view the movie. This date appears on the info screen of the movie. Once you start viewing the movie on your DVR, you have 24 hours to watch the movie again as many times as you want. After the 24-hour time period, you will no longer be able to view the movie on your DVR If you try to watch it after that time has expired, you will be prompted to delete the movie. You can always order the movie again the next time it is scheduled.