In the theme I’m using for vim, the strings are shown in red color but the problem is I have spellcheck on and the misspelled words are also shown in red color.
This makes it hard to see what is the mistake until you go to that word and delete any character.
I want to make the highlightation of the misspelled word in somewhat lighter then it currently. Say #ff2929.

You can use the
hi(short for:help highlight) command in your~/.vimrc. The general structure is:The
ctermis for terminal vim and theguiis for gVim. Thefgstands for foreground and is the color of the letters and thebgstands for background and is the color behind the letters.Terminal colors can be 0-15 for standard terminal colors (8 normal and 8 bright) or 0-255 for terms supporting 256 colors, like xterm-256colors. The gui colors are in hexadecimal format. xterm-color-table is a useful reference for both 256 and hexadecimal colors. The final option can be used to specify bold, italic, or none (neither).
In your case, it might be simplest to set the foreground to black to make the letters stand out. First, find a word that’s mispelled with
:set spelland then typing asdflkjasldf or something. Then type:hi SpellBad ctermfg=000 guifg=#000and see if that’s a solution you like. If not, use the xterm-color-table or another color reference to find a color you do like.