You don't need to — what you do, is issue them a uniform in a colour or pattern that fits the environment they will be operating in. All the rest of the colours and patterns can stay in warehouses.

The idea behind UCP was that it would be effective in as many environments as possible, thereby saving the cost of having to have multiple sets of uniforms in different colours and/or patterns. Unfortunately, it was only effective in a very limited range of environments, and elsewhere often stood out more than it blended in. I read things like US Army soldiers on exercise with those of other countries being told to stay behind so they wouldn't give the unit away purely by their uniform being so visible, for example. This video is quite telling in that regard:

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