Why do my pictures take on a blueish tint when i turn on manual mode?

[myabn]

I've been experimenting with my nikon d90 and when I have it on auto and it sets it at say, 1/10 exposure, 250 iso, and 2.2 aperture it takes a fine picture, but then when I switch it over to manual and set it at those same settings the pictures look blue??

 

[480sparky]

Check the white balance. It's probably set to Incandescent.

 

[analog.universe]

The white balance is likely also set to manual. Not familiar with Nikon, but on my camera I can still choose auto white balance, even in manual mode. Most times however I just use one of the presets, they get pretty close (and if none are close you can set it by hand using trial and error). If you set the white balance either by color temperature or by preset, then it remains consistent from shot to shot. Auto white balance will readjust every time you point the camera somewhere else. If you shoot in RAW, you can make adjustments to white balance after you've brought the photos to your computer.

 

[MrKarl]

I've been experimenting with my nikon d90 and when I have it on auto and it sets it at say, 1/10 exposure, 250 iso, and 2.2 aperture it takes a fine picture, but then when I switch it over to manual and set it at those same settings the pictures look blue??

Without looking at the picture, I can tell you it's your light source. Your digital camera has a white light balance. In auto, it does it on its own, in manual, you have to do it.
Let me recommend that you use a faster shutter speed if you are hand holding without a flash and use a smaller f-stop, unless you're doing head shots and even then, use something around a 5.6. If your pictures in manuel are blue using flash, then your camera is white light balanced for indoor tungstun lighting, say around 2,200 degrees Kelvin. Also, with daylight white light balancing, be very carefull of open shade, it too is very blue.