In one of my blog posts I mentioned that I was looking into colour coding my diary for various subjects. I ordered some Uniball Fine Eye pens which arrived today. I have used these pens before and they're really nice to write with.
Here's a picture showing the different ink colours:
And here's how I plan to store them in my Filofax, not sure how well this is going to work but we'll see! I've clipped them onto the business card holder at the front.