Compare the colour of spores mounted in Melzer's Reagent to the colour of spores mounted in water. The reaction should be immediate, but if in doubt about any colour change, leave for 20 minutes.

The reaction to Melzer's Reagent may be strengthened following pretreatment in alkaline solutions such as weak KOH or concentrated NH₄OH. Place lamellae in the alkaline solution, then remove and rinse in water prior to mounting in Melzer's Reagent.

Note: this character is only used if the Spore colour (microscope) state is either hyaline or pale, as the reaction is less obvious for darker pigmented spores.

Choose this state if: spores become bluish or violet to blackish blue when mounted in Melzer's Reagent. The reaction may be more pronounced for the spore ornamentation.