I removed stickers of my IELTS exam from my passport, and that left some white colour on my passport back page.
Will this cause me any problems when applying for a UK visa?
No, that should not cause any problem - the minor damage you describe doesn't meet the criteria for a 'damaged passport', which are:
A damaged passport is one which isn’t in a condition to be accepted as proof of identity.
Damage may include the following:
- details are indecipherable
- the laminate has lifted enough to allow the possibility of photo substitution
- discolouration to the bio-data page
- chemical or ink spillage on any page
- missing or detached pages
- the chip or antenna shows through the end paper on the back cover for the new style e-passports
- the chip has been identified as damaged after investigation