Each of the state folders contains an export.cfg file to control the appearance of the map when exported to Magellan eXplorist .imi format. There is also an export.cfg file in the \VectMaps folder, which controls the appearance of any map which is attached when the software is opened (I think).

Each of the state export.cfg files in my data are identical, but that in \VectMaps differs because as a part of my workflow, I try never to leave a map attached when exiting the software - I've found there to be fewer issues this way. MMO will modify that copy of the file in any case, as maps are attached and detached.
Here is what a standard export.cfg file for a state map looks like (with the settings I've chosen to format the maps for my own requirements):
;************************************************* **;
;* MobileMapper Office initialization file *;
;* DO NOT MODIFY THIS FILE! *;
;* *;
;* Copyright (C) 2003 Thales Navigation, Inc. *;
;* All rights reserved. *;
;************************************************* **;
;* Authored for MobileMapper Office (typ. export) *;
;* by Paul James Haydon / May 2012 (V5.0) *;
;************************************************* **;
[COPYRIGHT]
;** MAX 9 lines @ 23 chars for eXplorist XL! **
1= Map from .shp data:
2= OPENSTREETMAP:-
3=Data © OSM contributors
4= CC BY-SA
5=GEOSCIENCE AUSTRALIA:-
6=©Commonwealth Australia
7= (without liability)
8=Compiled by Paul Haydon
9= ver5.0 (17th May 2012)
[LAYERS]
NUMBER=22
;----- BOUNDARIES -------
0 = BDY-Suburb sub 0 8 0 9 0 0 0 8 0 8 0 0 0 7 0 8 0 0 0 6 0 8 0 0 0 5 0 7 0 0 MAGENTA MDASH_LINE
1 = BDY-State sta 0 9 0 9 0 0 0 8 0 8 0 0 0 8 0 8 0 0 0 8 0 8 0 0 0 7 0 7 0 0 RED MDASH_LINE
;----- WATER ------------
2 = Ocean ocn 0 9 0 9 0 0 0 8 0 8 0 0 0 8 0 8 0 0 0 8 0 8 0 0 0 7 0 7 0 0 CYAN SOLID_FILL
3 = Water wat 0 9 0 9 0 0 0 8 0 8 0 0 0 8 0 8 0 0 0 8 0 8 0 0 0 7 0 7 0 0 CYAN SOLID_FILL
4 = Islands isl 0 9 0 9 0 0 0 8 0 8 0 0 0 8 0 8 0 0 0 8 0 8 0 0 0 7 0 7 0 0 WHITE SOLID_FILL
5 = Rivers1 riv1 0 9 0 9 0 0 0 8 0 8 0 0 0 8 0 8 0 0 0 8 0 8 0 0 0 7 0 7 0 0 CYAN RIVER_LINE
6 = Rivers2 riv2 0 9 0 9 0 0 0 8 0 8 0 0 0 8 0 8 0 0 0 8 0 8 0 0 0 7 0 7 0 0 CYAN RIVER_LINE
7 = Coast cst 0 9 0 9 0 0 0 8 0 8 0 0 0 8 0 8 0 0 0 8 0 8 0 0 0 7 0 7 0 0 BLUE RIVER_LINE
;----- PARKS ------------
8 = Natural nat 0 9 0 9 0 0 0 8 0 8 0 0 0 8 0 8 0 0 0 8 0 8 0 0 0 7 0 7 0 0 PAIL_GREEN HEX_PATT
;----- RAILROADS --------
9 = Railway rly 0 9 0 9 0 0 0 8 0 8 0 0 0 8 0 8 0 0 0 7 0 8 0 0 0 6 0 7 0 0 ORANGE US_RAIL_ROAD
;----- CYCLEWAYS --------
10 = Cycleways cyc 0 6 0 9 0 0 0 5 0 8 0 0 0 4 0 8 0 0 0 3 0 8 0 0 0 2 0 7 0 0 RED MSOLID_LINE
;----- PATHS ------------
11 = Pedestrian ped 0 6 0 9 0 0 0 5 0 8 0 0 0 4 0 8 0 0 0 3 0 8 0 0 0 2 0 7 0 0 GREEN MSOLID_LINE
;----- ROADS ------------
18 = RD-Motorway mwy 0 9 0 9 0 0 0 8 0 8 0 0 0 8 0 8 0 0 0 8 0 8 0 0 0 7 0 7 0 0 YELLOW US_FEDERAL_HW_LINE
17 = RD-Trunk hwy 0 9 0 9 0 0 0 8 0 8 0 0 0 8 0 8 0 0 0 8 0 8 0 0 0 7 0 7 0 0 BLACK US_INTERSTATE_HW_LINE
16 = RD-Primary pri 0 9 0 9 0 0 0 8 0 8 0 0 0 8 0 8 0 0 0 7 0 8 0 0 0 6 0 7 0 0 BLACK US_STATE_HW_LINE
15 = RD-Secondary sec 0 9 0 9 0 0 0 8 0 8 0 0 0 7 0 8 0 0 0 6 0 8 0 0 0 5 0 7 0 0 DARK_GRAY US_MAJOR_RD_LINE
14 = RD-Tertiary ter 0 8 0 9 0 0 0 7 0 8 0 0 0 6 0 8 0 0 0 5 0 8 0 0 0 4 0 7 0 0 BLACK US_STREET_LINE
13 = RD-Other oth 0 7 0 9 0 0 0 6 0 8 0 0 0 5 0 8 0 0 0 4 0 8 0 0 0 3 0 7 0 0 LIGHT_GRAY US_STREET_LINE
12 = RD-Track trk 0 7 0 9 0 0 0 6 0 8 0 0 0 5 0 8 0 0 0 4 0 8 0 0 0 3 0 7 0 0 LIGHT_GRAY MDASH_LINE
;----- LOCATIONS --------
21 = LOCN-Cities cty 5 9 0 9 0 0 5 8 0 8 0 0 5 8 0 8 0 0 4 8 0 8 0 0 4 7 0 7 0 0 BLACK MAJOR_CITIES
20 = LOCN-Towns twn 5 9 0 9 0 0 5 8 0 8 0 0 5 8 0 8 0 0 4 8 0 8 0 0 4 7 0 7 0 0 BLACK LARGE_CITIES
19 = LOCN-Other min 5 8 0 9 0 0 5 8 0 8 0 0 5 7 0 8 0 0 4 6 0 8 0 0 4 5 0 7 0 0 BLACK MEDIUM_CITIES
[COLORS4BITS]
LAY_COLOR=0
[GROUPS]
NUMBER=8
SEARCH_GROUPS=6 7 6 1 2 5 4
0 = Boundaries 0
1 = Water 0
2 = Parks 0
3 = Railroads 0
4 = Cycleways 0
5 = Paths 0
6 = Roads 0
7 = Locations 0
[POI]
UNIT_PARAMS=0 8 0 9 0 0 0 7 0 8 0 0 0 6 0 8 0 0 0 5 0 8 0 0 0 4 0 7 0 0 BLACK NO_FILL
POI_INDEX=8
CAT_NUMBER=4
0=Hospitals, First_aid.bmp, FIRST_AID
1=Information, plus.bmp, PLUS
2=Schools, box.bmp, BOX
3=Train Stations, trstop.bmp, TRAIN_STATION
[ICS_FILE]
PATH_TO_ICS=Images\Ics\
The display shown here will not be particularly legible, due to the HTML formatting, but if you're interested, copy & paste into Notepad (or similar) or better still, open one of the state files once you have the data.
Anyway, the last two entries on each line in the [LAYERS] section (following the matrix of numbers) control colour and linetype (on the GPSr). To modify the appearance of the map, it is these two entries which will require editing. Refer to the following posts for details on each.
Cheers,
Paul.