zsh completion - partial coloring issues

test_color-completion-descriptions.zsh

# - start a clean shell with `zsh -f`
# - `source` this file

# - `a -<tab>`  WILL show color
# - `a --<tab>` will NOT show color
# - `b -<tab>`  will NOT show color
# - `c <tab>`   will NOT show color

# if you uncomment the line after "YYY", ALL examples WILL show color
#   first example shows up as expected (only option is red, rest is normal)
#   but for the others, the *complete* line will be colored
# if you uncomment the line after "ZZZ", ALL examples WILL show color (complete lines, as expected)

zmodload zsh/complist
autoload -U compinit && compinit

zstyle ':completion:*' list-separator "XX"
zstyle ':completion:*:default' list-colors '=XX*=31'
# YYY
# zstyle ':completion:*:default' list-colors '=^(XX*)=31'
# ZZZ
# zstyle ':completion:*:default' list-colors '=*=31'

_a () {
    _arguments \
      '(--first -f)'{--first,-f}'[first should be red]' \
      '--second[second should be red]'
}
compdef _a a

_b () {
    _arguments \
      '--second[second should be red]' \
      '-t[more red arguments]'
}
compdef _b b

_c () {
    local -a targets
    targets=(1:"this should be red" 2:"this as well")
    _describe -t targets 'stuff' targets
}
compdef _c c

I wanted to to colour the per-match description differently from the actual match. But for some reason I can't get this to work in different cases.

Using backreferences doesn't seem to work either ... but the results seem to be the reverse of the original, case a.2 & b & c work ... but a -<tab> fails.

the plot thickens: