In Putty, what do the colors on files and folders represent?

It's not putty - run the dircolors -p command it will tell you what color maps to each known file type.

It's not puTTY that does the coloring, it's likely dircolors. The specific will vary from distro-to-distro but you can get a good idea of how this works from man dircolors

For instance on my Debian install:

• Directories -> Dark blue
• Symlinks -> Cyan

You can also try echo $LS_COLORS to see what's stored in there. You will see the coloring rules in this variable.

This is from askubuntu.com by karthick87 (link)

Info

Run this when you're connected to a linux host and it'll output the colour scheme. Tested on Ubuntu 16.04 and CentOS 7.

Bash script

eval $(echo "no:global default;fi:normal file;di:directory;ln:symbolic link;pi:named pipe;so:socket;do:door;bd:block device;cd:character device;or:orphan symlink;mi:missing file;su:set uid;sg:set gid;tw:sticky other writable;ow:other writable;st:sticky;ex:executable;"|sed -e 's/:/="/g; s/\;/"\n/g')           
{      
  IFS=:     
  for i in $LS_COLORS     
  do        
    echo -e "\e[${i#*=}m$( x=${i%=*}; [ "${!x}" ] && echo "${!x}" || echo "$x" )\e[m" 
  done       
} 

Example output