doc: use colon for all color's rangs (GH-28998)

(cherry picked from commit 6b9f27d)

Co-authored-by: Rafael Fontenelle <[email protected]>

Author: miss-islington

Doc/library/tkinter.rst

@@ -644,8 +644,8 @@ callback
 
 color
    Colors can be given as the names of X colors in the rgb.txt file, or as strings
-   representing RGB values in 4 bit: ``"#RGB"``, 8 bit: ``"#RRGGBB"``, 12 bit"
-   ``"#RRRGGGBBB"``, or 16 bit ``"#RRRRGGGGBBBB"`` ranges, where R,G,B here
+   representing RGB values in 4 bit: ``"#RGB"``, 8 bit: ``"#RRGGBB"``, 12 bit:
+   ``"#RRRGGGBBB"``, or 16 bit: ``"#RRRRGGGGBBBB"`` ranges, where R,G,B here
    represent any legal hex digit.  See page 160 of Ousterhout's book for details.
 
 cursor