There are few things to note here (in addition to what was already said):
- Tires with a higher silica content are just sticker in the rain
- I have found Tourances to be very good in the wet
- Be SMOOTH imagine like you are riding on ice
- smooth is fast and smooth is safe
- Gentle on the front brake, little more of the rear. Always use both.
- Get good rain gear
- a comfortable rider is a safe one, you wont be cold or distracted
- Waterproof gloves, cold hands are the worse when wet
- Good helmet and visor - something that breathes well and doesn't fog up easily.
Basically you just have to adjust your speed to the conditions. A bike is less likely to hydroplane than a car for one major reason. PSI - there is more pressure on the contact patch of a bike than there is on a car. This has also been addressed by other posts above.
What to avoid:
Painted anything - lines, arrows, strips
If it looks shiny assume it is slippery
I ride year round and really enjoy riding in the rain. Once you learn to trust the bike and know what to expect it just becomes second nature.
Now lets talk about riding on ice....
Done that too but it is a completely different ball game.