In a detailed analysis of a group of initials (St Martial’s Bible, BnF Lat. 8,1-2, c. XIth), I try to explain the specific way people did concieve of a letter and its use in lecture in the middle-ages. The laws of colour use known from heraldry are operative in this XIth c. manuscript; they produce the peculiar pheno-type of a „letter-as-a-thing“. This type of a letter does not interpret its support as a screen (Anne-Marie Christin), but as a „campus“. This peculiar type is the result of a specific use of coulour and ist effects observable only on the original manuscript when presented in natural light, of which it is possible to give a precise functional description: the use of the fundamentals gold and purple, of minium, of green (ground field especially for ornamental motives) and blue (ground field for figures). All this permits to point to a peculiar reading effet produced by this kind of initials I here call, litterally, the pro-blema.