Subj : Advanced terminal type
To   : GitLab note in main/sbbs
From : Michael J. Ryan
Date : Sun Sep 13 2026 00:48:17

https://gitlab.synchro.net/main/sbbs/-/issues/1141#note_10350

The DECRQSS probe — set an odd RGB value, then read back what the terminal actually stored:
Send ESC[48;2;1;2;3m (background to rgb(1,2,3) — no palette entry matches).
Send ESC P $ q m ESC \ (DECRQSS request for current SGR).
Read the reply: ESC P 1 $ r <params> m ESC \.
If the params echo 48;2;1;2;3 (or 48:2::1:2:3), you have real truecolor. If they come back as 48;5;n or nothing color-ish, the terminal quantized to the 256-color palette. Reset with ESC[0m after.
--- SBBSecho 3.37-Linux
 * Origin: Vertrauen - [vert/cvs/bbs].synchro.net (1:103/705)

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