Disclosed herein is a method of endoscopic diagnostic evaluation of pathologies of the gastrointestinal tract in a subject, said method comprises administering to the subject a diagnostically effective amount of at least one solid composition of claim 1 within a 24 hour period preceding the endoscopic diagnostic evaluation and endoscopic diagnostically evaluating the gastrointestinal tract for said pathologies, wherein said solid composition is for oral administration and comprises: (a) at least one dye selected from among methylene blue, congo red, carmine indigo, toluidine blue or mixtures thereof； (b) a first matrix in which said at least one dye is incorporated, wherein said first matrix comprises: (i) at least one lipophilic compound selected from among saturated, unsaturated or hydrogenated long chain alcohols, saturated or unsaturated or hydrogenated fatty acids, salts thereof, esters or amides, mono-, di- or triglycerides of fatty acids, polyethoxylated derivatives thereof, waxes, ceramides, cholesterol, cholesterol derivatives or mixtures thereof having a melting point below 90°C and (ii) at least one amphiphilic compound selected from among polar lipids of type I or II (lecithin, phosphatidylcholine, phosphatidylethanolamine or a mixture thereof), ceramides, glycol alkyl ethers (such as for example, diethylene glycol monomethyI ether), alkyl sulfate or sulfosuccinate salts or mixtures thereof； (c) a second matrix comprising at least one hydrophilic compound selected from among polymers or copolymers of the acrylic or methacrylic acid, alkyl vinylpolymers, alkyl celluloses, hydroxyalkyl celluloses, carboxyalkyl cellulose, modified or plurisubstituted celluloses, polysaccharides, dextrins, pectins, starches, complex starches and starch derivatives, alginic acid, synthetic rubber, natural rubber, polyalcohols or mixtures thereof, wherein the first matrix is dispersed in the second matrix； (d) optionally other physiologically acceptable excipients； and (e) opt
