Spot Channel Help

I was just wondering if someone can answer this for me.

Why is it when i am producing a document that uses two spot channels, both the channels actual colours are displayed on screen.

But...

If i am working on a document that has only one spot channel, the channel is black

'Cos one spot channel (in multichannel mode) don't produce composite channel which could be displayed in colors. In this case you see spot channel just as separation plate. But you can turn Preferences > Display & Cursors > Color Channels in Color ON.