Found a solution.
Here it is, in case anyone hits the same wall as I had  
Sub Main
Dim oDoc as Object, oSheet as Object, oCell as Object
Dim oTextCursor as Object
	oDoc=ThisComponent
	oSheet=oDoc.getSheets().getByindex(0)
	oCell=oSheet.getCellByPosition(0,1)
	oCell.String="The Moon is in synchronous rotation with Earth, always showing the same face with its near side marked by dark volcanic maria that fill between the bright ancient crustal highlands and the prominent impact craters. It is the second-brightest object in the sky, after the Sun (measured by illuminance on the surface of the Earth)"
	with oCell
		.CharFontName = "Arial"
		'.CharPosture = com.sun.star.awt.FontSlant.ITALIC
		.CharHeight=12		
	end with
str_length = len (oCell.String)
str_searched = "ea"
str_searched_length = len (str_searched)
oTextCursor = oCell.createTextCursor()
	
for i = 1 to str_length
	found = instr (i, oCell.String, str_searched)
	if found > 0 then
			With oTextCursor
				.gotoStart( False )
				.goRight(found-1 , False )  
				.goRight(str_searched_length, True )
				.setPropertyValue("CharColor",0099000)	
				.gotoEnd( False )
			End with
		i = i + found+str_searched_length
	endif
next i
End Sub