difftastic do not show color in fzf preview

[dsypasit]

I tried to use difft to show the difference inside fzf. In the previous script, it showed colors but not in difft. However, when I used 'git show', it displayed correctly. What's wrong with it?

previous script

git log --oneline --format="%C(auto)%h %s%d" | fzf --ansi --preview "git show --color=always {1}" --bind 'enter:become(echo {1})'

using difftastic

git log --oneline --format="%C(auto)%h %s%d" | fzf --ansi --preview "GIT_EXTERNA_DIFF=difft git show --color=always {1} --ext-diff " --bind 'enter:become(echo {1})'

difftastic version

dotfile on  main [!⇡]
❯ difft --version
Difftastic 0.58.0 (0c9277108 2024-05-10, built with rustc 1.78.0)