I assume this is a bug. The Scarlet and Green Cabochon seems to allow my rogue to add 1d10 to ranged attack rolls, all of the time, just by revealing it. I certainly makes the game easier, but it seems like a bug to me.

Upon further testing, the bug only applies when I have the Black Arrow long bow, which does have a strength modifier...but a combat one.

Upon further testing, the bug only applies when I have the Black Arrow long bow, which does have a strength modifier...but a combat one.

I observed the same, but never tried ranged weapons (I was using it with Kyra and Amiri). Strangely, the Cabochon can be used even with Holy Light, which is a complete nonsense (not even Melee check) and should be corrected.

Apparently the Black Arrow bow has a melee flag checked. I just used a boon to boost a melee or fortitude attack by 2 or anything else by one....and it got the +2 dice. Another bug found I guess!

Rejoice! Now the item cannot be used in combat. Problem solved.
Valeros and Amiri are sad but I guess sometimes sacrifices must be made for the greater good.

Joking aside I haven't actually tested if this works in non combat melee checks; only that it doesn't work with combat melee ones. The item still works with fortitude checks.
Oh well, the item was too OP for combat.