The colours used are decided by the person who installed it, there is no "specific colour guide" It is unusual to have a 3 core and earth, so the question is what was there before you decided to add the light. The one with the red mark could be live or it could be switched live, and in any case which is the neutral. Unless you can find the other end of the cable and take it from there, I would suggest you call in a competent person to do the job for you. (It doesn't have to be an electrician) And never rush / do something you are not competent with as unlike water where you get wet, electricity kills and does not give a second chance.
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