map plotting

Hello,
I have a code that plots the coordinates in a global map. I just
wanna
use the same procedure but i need differentiate the coordinates with
different colors and I tried using color tables but its not changing
color of any of the points that is on the map. Can anyone help me fix
this? I'm appending the code that I have to plot these points on the
map.. All I want is to change the color of the points that I have on
the map. The code below just plots the asterisks on the map... I just
wanna change the color of those asterisks.
Thanks,
Mahesh
---------------------------------------------------------------------------**-------------------------
LOADCT, 26
;color_tab = [0,2,20,31,42,47,50,55,60, 65,80,89,96, 100,109,112,
114,127,130,133,144,$
;169,183,192,199,210,214,3, 10,230,240,246,255,203,142,157]
set_plot,'ps'
;!p.font = 0
;device,filename=strmid(file3,56,19)+'timeseries'+ '.ps'
device,filename=strmid(file3,56,23)+'timeseries'+' .ps'
;plot,findgen(100),/nodata,background=!d.n_colors-1
;!P.background=!d.n_colors-1
map_set , /hammer,limit = [-40,-180,40,180],color=0;,/hires
;map_set , /mercator,limit = [0,50,40,100],color=0

map_continents,/continents,/countries,color=0
oplot,lon,lat,psym=2,symsize=1.0,color=25
oplot,[-180,180],[0,0],color=180,linestyle=1
map_grid, color=0,latdel=10,londel=20
---------------------------------------------------------------------------***----------------------------------