If what you were seeing were truly grey, then all you’d need is a brighter light source to detect the difference. However, I expect that what you’re looking at has traces of colors. The subtle differences would be best seen with a high CRI beam.
There’s a group buy for one now: 3rd batch produced!! GBGB: 2nd batch of BLF-348 (Classy and Small 1xAAA Stainless Steel light, with Nichia NVSW219B-V1 R9050)!