My friend, previously a photographer, said that if you are taking photos in cold weather the photo is more blue (as if a slight blue filter has been applied). Inversely, taking photos when it is warm — the photo will have a reddish tone. He argues that this is dependent solely on (ambient, not color) temperature.
I would be interested in knowing if this is the case, and if so, why.
I think he, or you, are mixing up "colour Temperature" with actual colour.
There are many factors that can affect how a photo looks, however actual ambient temperature is not one of them.
The main factor that affects colour in photography is the composition of the incident light. What is referred to as "cool" means the light source has a blueish tint, a "warm" light source has a reddish tint.
Colour temperature (and in turn White Balance, which you can set in digital photography or by selecting different film) can be used to imply warm or cool weather:
e.g. Beach scene = warm, with yellows (sand etc)
Skiing scene = cool, with mostly blues from the sky and whites from the snow.
Your friend may have been referring to film photography, otherwise his assertion is just silly.
The sensitivity of film varies somewhat with temperature. Color film is really three separate sensitive layers in the same film. Each of those can vary differently with temperature. There could therefore conceivably be a slide film where the sensitivity of blue drops off less quickly with cold than does the sensitivity of green and red.
For color negative film, this assertion is again silly because nobody would expect color negative film to record absolute color anyway. It would be relative to some white or gray reference shot at the scene with that lighting at that temperature, so differences in the sensitivity of the magenta, cyan, and yellow layers wouldn't matter. The differences from batch to batch would probably be larger than between a cold and hot day outside anyway.
I think you're friend was getting confused, colour temperature is different to ambient temperature. Blue is classed as 'cool' and red is 'warm'.
Different light sources have a different 'colour temperature', eg LED lights, fluorescent tubes and energy saving bulbs often tend to be 'cool', incandescent lights tend to be 'warm'.
Purely by coincidence it often corresponds with the physical temperature (ie: incandescent bulbs are too hot to touch whereas fluorescent tubes and LEDs can often be touched while they're on (don't try that though!)).
The white balance function in a camera or editing software is designed to correct this, I think by using known 'colour temperatures' on the Kelvin scale.
Try searching Google Images for 'colour temperature scale' and you will get some good ideas about where different light sources fall on it
