You can find the list of Registration Codes via the Manage Register area (Register > Manage Register > view register) or on the Student Profile > Attendance Tab > Attendance Codes. (It will direct you to the article Registation Codes). At the base of the table you can see which codes are counted and what categories they fall into.
The colour coding in here is for how each attendance code is counted;
Blue - This means the code is counted as a "Present mark" and will positively effect the attendance figures.
Yellow - These codes are counted as an Authorised Absence, this will negatively effect the attendance, but will show that the absence was authorised by the school.
Orange - These codes are counted as Approved Educational Activity this is counted as present so will positively effect the attendance figures.
Pink - These codes are counted as an Unauthorised Absence, this will negatively effect the attendance and show that this absence was not authorised by the school.
White - These codes are not counted towards any attendance calculation so will not effect the attendance figures at all.