Hydrogen peroxide vapor in detergent and pharmaceutical powders can have detrimental effects on enzymes and active ingredients. Potassium titanium oxide oxalate (PTO) adsorbed into cellulose pellets changes color upon exposure to hydrogen peroxide vapor. TGA and DVS analyses showed that cellulose dominates the interactions of PTO-loaded pellets with humidity, while the pure PTO salt can form either a mono- or dihydrate and deliquesce above 80% RH. The mono- and dihydrate forms of PTO salt gave different changes of the surface reflectance colors after exposure to hydrogen peroxide vapor. SEM-EDX and μ-CT scans showed that titanium move towards the surface of the PTO Pellets after reaction with hydrogen peroxide further affecting the surface reflectance. It is concluded that PTO-loaded pellets are suitable for detection of hydrogen peroxide vapor at an interparticle level in powders with humidity conditions in the range of 10 to 80% RH.