Black and white only

[TribbleSmasher]

The A600 is was one of the first machines experiencing damage from leaking electrolyte capacitors, destroying parts of the main board or just not working anymore.

Since you've tried multiple connections and all resulted in b/w instead of colour video, my guess is:
Capacitor damage.

Fix it. as soon as possible, as it only gets worse.

[TribbleSmasher]

You might start with Youtube searching "Amiga 600 recap".

there are people in the community doing it for you, but you need to be close to one to avoid shipping the computer around.

Also professional repair shops are an option.