I was recently customizing my D5100 and set the ISO Sensitivity to AUTO while selecting Playback Display Options @ None, RGB, and Shooting data. I have since noticed several ISO readings in red during playback. It seems as though the red appears in ISO readings of 800 or higher. RGBs look normal. Is this a 'warning' that the given photo may be susceptible to a grainy effect?
#2. "RE: Auto ISO sensitivity" In response to Reply # 1
Thank you Joseph for the manual page references. (yes, I printed the 240+ page manual out some time ago). I took several more photos and the 'red' does indicate the use of auto ISO. I'm just playing with the ISO sensitivity settings for now (ON, Max 6400, Min 1/30) while in A (aperture) mode.
Page 155 indicates that ISO sensitivity is adjusted 'if' optimal (200) exposure can not be achieved.