I haven't tried to meditate in a long time, but my understanding of the process was, setting aside mysticism and tradition, you just take a mental concept and you focus on it and every time your mind starts drifting you return to it.

So, I've heard that people make a big deal about choosing a mantra, but my thinking was it can be anything, and somehow I got into the habit of visualizing a blank field of a particular color. The nice thing about focusing on a color was that if my visual imagination distracted me, I could concentrate on "seeing" the color, while if I was imagining words or sounds, I could focus on the name of the color too. So it was like having an object to focus on that had all the different angles available.

I'm not sure I've never experienced synaesthesia, but I'm pretty sure I haven't been perceiving smells or sounds as having color recently.