Screen settings, lighting, camera exposure and the background can all affect a colour comparison. Reflective finishes add viewing angle as another variable.
Reduce the variables
Compare products on the same screen and under the same viewing conditions. Use the original product photographs rather than unrelated reposted images.
Use a physical reference
When an exact match matters, compare a physical swatch with the intended outfit or reference. An RGB similarity is not a promise of an identical cured result.