Red is for ship to ship, blue is for squadron. What is the black dice for ? and can it be use against squadron?

Alas its not quite that cut and dry. The little diamonds on your ship cards will tell you what colors and how many to use for each facing on a ship, and how many for anti-squadrons. For instance, your Victory I class has 3 red and 3 black in its front arc.

All 3 colors are used in ship to ship, and so far I think blue and black are used in squadron v squadrons. All colors are used in squadrons to ships, and so far only blues in ships to squadrons (with black on the way)

Each color die acts differently. Reds have a bit of everything. Blues have no blanks. Blacks are about raw damage output.

In general the dice correspond to range bands. At long range, only red dice can be used. At medium range, red and blue dice can be used. At close range, all 3 colors can be used. This is indicated on the range ruler by the colored diamonds in each range band. For ships with mixed color batteries, as they enemy moves closer, they can roll more dice against them due to the closer range band.

I find it more useful to think about how each color behaves (see earlier) than what situations the dice is used in (ship to ship, squadrons etc) An all blue ship will always have a useful attack since there aren't any blanks, but they can't do anything at long range. A black/red ship really wants to be up close, otherwise its most powerful dice aren't doing much.

All dices work on ships and squadrons.

You use:

Red: at long range (medium and shot too)

Blue: at medium range (short to)

Black: at short range

Of course you can only use the dice you have in your batteries.

When attacking ships you roll the dices in your hull battery. With squads you use the anti-squad battery.

An all blue ship will always have a useful attack since there aren't any blanks

I think you will find rolling nothing but acuracy to be less then useful though