1. Chromo-endoscopy with methylene blue 0,1% (groups A-C-E) An Olympus spray catheter is used through the biopsy channel of the endoscope to apply the dye, a saline solution with methylene blue in a concentration of 0.1%. This technique was already validated in previous studies. Besides the extra time needed for dying the entire colon mucosa, no other manipulations are needed for this technique. Moreover, the time needed to dye can be recovered because only chromo-endoscopy guided biopsies will be taken instead of random biopsies throughout the colon, which normally also requires a considerable amount of time. Previous studies using chromo-endoscopy versus conventional screening colonoscopy did not show a significant difference in total procedure time. The endoscopes used do not differ from the ones used in the other randomization arms and include either an Olympus H180Q colonoscope, Fujinon EC 590 ZW/M colonoscope or a Pentax 3890i colonoscope. All three endoscopes are CE approved and are commercially available.