highlighted comments with spelling errors

[JinraeKim]

Terminal Emulator Info

iTerm2

Output From vim --version

➜  FlightSims git:(update-README-add-lqr-ex) ✗ vim --version
NVIM v0.5.0-dev+0c7610c
Build type: Release
LuaJIT 2.1.0-beta3
Compilation: clang -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=1 -DNDEBUG -Wall -Wextra -pedantic -Wno-unused-parameter -Wstrict-prototypes -std=gnu99 -Wshadow -Wconversion -Wmissing-prototypes -Wimplicit-fallthrough -Wvla -fstack-protector-strong -fno-common -fdiagnostics-color=auto -DINCLUDE_GENERATED_DECLARATIONS -D_GNU_SOURCE -DNVIM_MSGPACK_HAS_FLOAT32 -DNVIM_UNIBI_HAS_VAR_FROM -DMIN_LOG_LEVEL=3 -I/tmp/neovim-20210226-60580-1jrn53o/build/config -I/tmp/neovim-20210226-60580-1jrn53o/src -I/opt/homebrew/include -I/opt/homebrew/opt/luv/include -I/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include -I/opt/homebrew/opt/gettext/include -I/tmp/neovim-20210226-60580-1jrn53o/build/src/nvim/auto -I/tmp/neovim-20210226-60580-1jrn53o/build/include
Compiled by [email protected]

Features: +acl +iconv +tui
See ":help feature-compile"

   system vimrc file: "$VIM/sysinit.vim"
  fall-back for $VIM: "/opt/homebrew/Cellar/neovim/HEAD-0c7610c_1/share/nvim"

Run :checkhealth for more info

Issue Description

The comments with spelling errors are highlighted too much.
For example, in the following picture, some comments (e.g., approximator) are highlighted in red.

[JinraeKim]

It can be customised.
In my case, I read this post.