You have references to /K (instead of /H) in the /H documentation. Thanks for the awesome plugin.
/H:color allows you to set the colors used to highlight found text. color may be an integer value (prefix 0x for hexadecimal) or a quoted string. For example, /K:0X1E or /K:"BRIGHT YELLOW ON BLUE" will cause matching text to be highlighted in bright yellow on blue. /K:0 or /K:REVERSE shows matching text in reverse video. Note that the plugin will pick different colors if the matching text has the same background color as the one you specify.