[embee]

Coolant really does 2 things, the anti-freeze bit and the corrosion protection.

The anti-freeze used in auto coolants is almost always ethylene glycol. There are snake oil merchants who try to sell propylene glycol as a wonder product, but no-one in the automotive sector to my knowledge (40yrs in the industry) uses it, prop glycol is used mainly in the food industry as coolant since it is not toxic, whereas ethylene glycol is very toxic. Use a regular auto coolant in an automotive application.
The best antifreeze effect for ethylene glycol is at around 50/50(ish) mix with water, use deionised or at least very soft water, clean rain water is fine usually, be careful with tap water, generally not recommended but OK if nothing else is available.

The inhibitor aspect is far more complex, different additives are used for different applications and specific purposes with mixes of materials or gas contamination and wet liner cavitation etc (big diesels etc).

Most Japanese bikes specify a silicate free coolant to avoid pump seal wear. The label or tech data sheet will tell you if it is silicate free.

Colour is not a significant aspect, it is a dye, but common practice is that longer life coolants tend to be pink/purple etc. Not guaranteed, but typical.

For most of my engines, bikes/cars, I have ended up using Comma G30, it is based on BASF Glysantin 30 which is a major industry product and silicate/borate free.
Halfords long life is often recommended by folk for typical bikes, and as far as I know is silicate free and a perfectly good product.

As said by others, fill at the radiator cap right to the top. When it heats up some will be pushed out into the "make-up" bottle, and drawn back into the system when it cools down again. Keep the make-up bottle between the max and min marks when cold. A couple of cycles should stabilise it.

Tap water is fine for flushing the system through unless you know it is very hard. If old coolant smells manky it means the additive pack has probably expired, flush and renew every few years as routine, it's cheap.