SoilColorDict soilcolorDict;
  bitmap = al_create_bitmap(soilGrid->getWidth(), soilGrid->getHeight());
  al_lock_bitmap(bitmap, al_get_bitmap_format(bitmap), ALLEGRO_LOCK_READWRITE);
  for (int y = 0; y < soilGrid->getHeight(); y++)
    for (int x = 0; x < soilGrid->getWidth(); x++)
      {
      al_put_pixel(x, y, soilcolorDict.getColor(soilGrid->ref(x, y).getTopsoilType()));
      }
    al_unlock_bitmap(bitmap);

Here, an object that stores ALLEGRO_COLORs in a std::map is created (soilcolorDict). The bitmap, which is a global variable, is assigned an ALLEGRO_BITMAP and is filled by fetching colors from soilcolorDict. A delve with debugger confirms that ALLEGRO_COLOR objects are being retrieved, each filled with color information.

The constructor for soilcolorDict looks like

A bunch of key-color pairs are inserted into the map, after al_init() and the other functions are called.

Next, in the rendering part of the function,

al_set_target_bitmap(al_get_backbuffer(root));
  al_clear_to_color(al_map_rgb(250, 0,254));
  al_draw_bitmap(bitmap, 0, 0, 0);

is executed. The backbuffer, which is cleared to a magenta just so I can see the contrast, gets blitted to by a bitmap.

Finally,

al_flip_display();

Problem: the screen looks like this.

{"name":"iGRJBWr.png","src":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/d\/7\/d73e3ad75f78d73dc875fa99314b540d.png","w":656,"h":518,"tn":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/d\/7\/d73e3ad75f78d73dc875fa99314b540d"}

When I add

al_set_target_bitmap(bitmap);
  al_clear_to_color(al_map_rgb(0,255,0));

before setting the target to the backbuffer, the screen looks like

{"name":"HVchHqc.png","src":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/c\/4\/c47f3f1a7bdcdbe64e56ef2a9cefdc2e.png","w":656,"h":518,"tn":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/c\/4\/c47f3f1a7bdcdbe64e56ef2a9cefdc2e"}

It leads me to guess that I'm doing something wrong when drawing to the bitmap, but I can't tell why. Been at this a couple of hours and I can't really make progress :<

The exact way the functions are implemented is that there is a framework that provides the functions

init() // Installing keyboards, setting FPS, installing addons...
  userDefinedInit() // Anything else you want to do before starting the game loop.
while loop
  catchEvents()
    update()
    render()
destroy()

Everything except the render code is in init(). Help would be greatly appreciated! D:

Seems to me that you're missing al_put_pixel needs the target bitmap to be set to bitmap....try al_set_target_bitmap(bitmap) before you nested for loops.

... That seems like quite the stupid mistake. In fact, I'be done exactly the same loop but WITH the set_target done in another project >_> Not at PC, but I' pretty sure that'll fix it. Will return if it doesn't, within 25 hours ;3

I'm still looking at your code, but I did notice 2 things at least - you don't need to use insert on a std::map - using the map indexing method is cleaner. Same code behind the scenes, but it looks better to use colors[stClay] = al_map_rgb(64,127,0);. The second pkrcel already pointed out - you have to set the target bitmap before drawing to it, or you will be drawing to whatever was set to the target bitmap previously.