Create a wall of text or symbols on 1 layer, make sure there's enough to cover the entire canvas. Rasterize that layer once you have it all done by right clicking on it and selecting rasterize.
Place the larger version of the symbol/letter/object on another layer (can be anything you want), ctrl click the thumbnail for that new layer to select just the object and not the whole layer. Hide that layer by clicking the eye.
Click the layer with the wall of text on it, you should still see the white dots like you've selected an invisible object. Cut and use paste in place (in the edit menu), then adjust the object a little so it fits in with the wall of text.
Then you can fiddle with the colours all you want, you can change transparency etc... The layer you cut will need to have a colour overlay. You could also try using a clipping mask which allows easier editing later on but for now method will work.