There a few things that can cause your hair extensions to discolour such as:
Hard Water :
If you live in an area where there is high iron content in your water then this can cause hair
Suncreen : Sun tan lotions contain a chemical called avobenzone, which protects against UV rays. In order to ensure the longevity of the protection suncreens also contain octocrylene. These are both active ingredients and when exposed to the sun and hard water when you're washing your hair it causes a chemical reaction, which will then turn your hair orange or pink.
The only way to avoid this happening is to tie your hair back securely and avoid playing/touching with it during the day. Even with suncream on your hands it can transfer onto your hair.
Using heated tools too often, on a high heat and without using heat protection spray call all contribute to hair discoloring. Limit styling to once/twice a week, always use heat protection spray and never go above 180 degrees on heated tools.