When taking infrared photos sometimes the images that come from the camera are monochrome, sometimes they have weird colours. Usually this is affected by the combination of filter type and the camera sensor, although you can always make a monochrome image from a colour original.
However the colour images do not show the same colours our eyes will see: that’s the nature of infrared (non-visible) light. So we often refer to these as “false” colours, and there can be some artistry in mapping them to visible colours that look pleasing.
When you start out you may begin with images from the camera that just seem to be only various shades of red, but by colour-balancing the image in Photoshop you can often extract blues and other colours from the variations, then shift those to interesting colours. A long time ago I wrote a Photoshop action (well, I built upon a technique I saw demonstrated by someone else) to help with this, and apparently it’s still in use by many folks today. For anyone looking for the FalseColoursAction, a ZIP file can be downloaded here (this article was prompted by a reader searching for the old action). Do note however that the processing in that Photoshop action is purely “by the numbers”, and the visual results will be different depending on the colour space (ProPhoto, AdobeRGB, etc) you’re using.
Here you can see a source image (a Nairobi hotel pool-side) along with the result of some Photoshop manipulation.
If you’re capturing IR photos in RAW mode you may also be interested in the options to use custom DNG profiles to bring the White Balance sliders back into reasonable ranges and start off with images without significant overall colour casts. The article I wrote on this in 2009 is still relevant today. I currently have a modified EOS M2 camera I can use with all my Canon-mount lenses for infrared imaging, and I have a custom DNG profile defined for each IR filter I use with the camera, and the images are managed in Lightroom alongside all my visible-light images from other cameras.
The following two images only differ by the DNG profile used: the first is using a standard profile, and the Temperature/Tint sliders can’t move far enough to neutralise any colours in the image. These copies have not had any Photoshop processing applied to them yet.