the RED cross is CANARY YELLOW

Maltese cross

location unknown

THE RED CROSS

The Red Cross

The Red Cross diamond is a cushion shaped, canary yellow diamond weighing 205.07 carats. When it was discovered in one of the De Beers mines in South Africa in 1901, it weighed 375 carats. When put under a brilliant light, this diamond absorbs part of it and subsequently becomes phosphorescent (self-luminous) in the dark. Another thing that distinguishes this stone is that on the upper facet, the shape of the Maltese cross is clearly visible.

Cut in Amsterdam, the stone was offered by diamond dealers at an art sale held in London in 1918 under the auspices of Christie's, for the benefit of the Red Cross. Since then it has re-appeared from time to time during auctions, for example in Tokyo in 1973 where it was withdrawn, its reserve price not having been reached. Its current owner is not known.

https://www.langerman-diamonds.com/encyclopedia/history-of-natural-color-diamonds/famous-color-diamonds/redcross.html