If you try to change, then you must try and try becouse some color overlap.
You can open navigon theme and copy/paste html code for road and you will see difference.
For change building color you must change this two area:

<?xml version="1.0" encoding="UTF-8"?>

<GARMIN_MAP_THEME>
<METADATA>
<TITLE>Nederland</TITLE>
<DESCRIPTION>Theme for Nederland (Netherlands).</DESCRIPTION>
<LOCALELIST>
<locale>Nederland</locale>
</LOCALELIST>
<Version><Major>2</Major><Minor>20</Minor></Version>
</METADATA>

<PRESENTATION ID="Guidance">

<STYLELIST>

<STYLE field = "MAP_BEACH_CLR" >
<COLOR >
<PRIMARY day = "#E8C455" night = "#67491D" />
</COLOR>
</STYLE>

<STYLE field = "MAP_BUILDING_CLR" >
<COLOR >
<PRIMARY day = "#ECECC4" night = "#26003B" />
</COLOR>
</STYLE>

<STYLE field = "MAP_BUILDING_SHADOW_CLR" >
<COLOR >
<PRIMARY day = "#C8C8A7" night = "#3B005A" />
</COLOR>
</STYLE>

<STYLE field = "MAP_EXTRD_AREA_CLR" >
<COLOR >
<PRIMARY day = "#788181" night = "#323F48" />
</COLOR>
</STYLE>

<STYLE field = "MAP_GLACIER_CLR" >
<COLOR >
<PRIMARY day = "#FFFFFF" night = "#808080" />
</COLOR>
</STYLE>

<STYLE field = "MAP_LAND_CLR" >
<COLOR >
<PRIMARY day = "#A4E666" night = "#4B4B4B" />
<SECONDARY day = "#A4E666" night = "#4B4B4B" />
</COLOR>
</STYLE>

<STYLE field = "MAP_MISC_AREA_CLR" >
<COLOR >
<PRIMARY day = "#CCCCCC" night = "#472835" />
</COLOR>
</STYLE>

<STYLE field = "MAP_MISC_RESTR_CLR" >
<COLOR >
<PRIMARY day = "#808080" night = "#FFFFFF" />
</COLOR>
</STYLE>

<STYLE field = "MAP_MISC_OBSTR_CLR" >
<COLOR >
<PRIMARY day = "#808080" night = "#FFFFFF" />
</COLOR>
</STYLE>

<STYLE field = "MAP_MISC_WATER_AREA_CLR" >
<COLOR >
<PRIMARY day = "#3399FF" night = "#002868" />
</COLOR>
</STYLE>

You will find this area 4x in KTMF, so you must change with same parameters 4x
For editing KTMF you must have time and patience and a lot of testing on nuvi.