Do you mean colorimetric? I can suggest a very sensitive fluorescence-based method to detect the nucleoside diphosphate product that can be done in multiwell plates (Anal. Biochem. 415: 190-196. 2011). Alternatively, if you attach a fluorescent label to the peptidoglycan (on the Lys or Dap amino acid), you could follow glycosylation by HPLC with nM sensitivity. Without the fluorescent dye, you could still follow the process by HPLC using 260 nm absorbance with micromolar sensitivity.