Fix dimming of indexed colors

It seems like the list of colors might have changed a bit, leading to
indexed colors not being transformed into their dim colors correctly.

To prevent this from happening in the future, the dimming for colors in
the range '0..=7' is now performed by offsetting them from the
'NamedColor::DimBlack'. Since this is the first dimmed color, this
should always work as long as all dimmed colors are added in the correct
order.

CHANGELOG.md

@@ -23,6 +23,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Wide characters sometimes being cut off
 - Preserve vi mode across terminal `reset`
 - Escapes `CSI Ps b` and `CSI Ps Z` with large parameters locking up Alacritty
+- Dimming colors which use the indexed `CSI 38 : 5 : Ps m` notation
 
 ### Removed
 

alacritty_terminal/src/term/mod.rs

@@ -401,7 +401,7 @@ impl RenderableCell {
                 ) {
                     (true, Flags::BOLD, 0..=7) => idx as usize + 8,
                     (false, Flags::DIM, 8..=15) => idx as usize - 8,
-                    (false, Flags::DIM, 0..=7) => idx as usize + 260,
+                    (false, Flags::DIM, 0..=7) => NamedColor::DimBlack as usize + idx as usize,
                     _ => idx as usize,
                 };