bug: Lazy window backdrop distorts colors with notermguicolors

[j4ns8i]

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• I have searched the existing issues of lazy.nvim
• I have searched the existing issues of plugins related to this issue

Neovim version (nvim -v)

v0.9.5

Operating system/version

MacOS 13.6.6

Describe the bug

With notermguicolors, the new Lazy window backdrop distorts the colors and makes it unclear that it's a backdrop.

Steps To Reproduce

Run :Lazy with notermguicolors and a colorscheme that uses cterm colors, like "pablo".

Expected Behavior

I would expect this feature to be disabled when notermguicolors is set, because blending the colors isn't straightforward when users use cterm colors 0-15 as their primary colors.

Repro

-- DO NOT change the paths and don't remove the colorscheme
local root = vim.fn.fnamemodify("./.repro", ":p")

-- set stdpaths to use .repro
for _, name in ipairs({ "config", "data", "state", "cache" }) do
  vim.env[("XDG_%s_HOME"):format(name:upper())] = root .. "/" .. name
end

-- bootstrap lazy
local lazypath = root .. "/plugins/lazy.nvim"
if not vim.loop.fs_stat(lazypath) then
  vim.fn.system({ "git", "clone", "--filter=blob:none", "https://github.com/folke/lazy.nvim.git", lazypath, })
end
vim.opt.runtimepath:prepend(lazypath)

require("lazy").setup({}, {
  root = root .. "/plugins",
})

vim.o.termguicolors = false
vim.cmd.colorscheme("pablo")

[j4ns8i]

FWIW, I resolved this issue by setting ui.backdrop to 100 in my init.lua:

require('lazy').setup('plugins', {
  ui = {
    backdrop = 100,
  },
  -- <snip> --
})

[j4ns8i]

For convenience, here are images from reproducing this behavior:

Normal view:

After :Lazy:

The text in the background turned mostly green, but no less vibrant, which is why it's hard to identify as a backdrop.