It is totaly normal to obtain such result after the concentration of phenolic extract using a rotavapor. From my experience in extraction and concentration procedures, I thing that there is no problem in having black concentrate after évaporation of the solvent
Several extracts have this final aspect, but to say if it is normal also other info are necessary. I.e. The nature of extracted plant material, the used solvent, the temperature applied during evaporation, the aspect of the starting solution (color).
Anyway, the phenolics should be concentrated at the bottom of the flask and their color is brown (this could be consistent with the color assumed by yellow-orange compounds in concentrated form). The other substances at the top of the residue seems of green color and may likely be chlorophylls and/or related compounds.