Wiring – Changing light fixture and wanting to know colour codings for cables

It sounds wrong to me, but I couldn't be sure without actually being there. You should connect the new fixture, in exactly the same way the original fixture was connected.

If there wasn't a grounding conductor in the original circuit, replacing the fixture did not make one magically appear. If a grounding conductor is required, you'll have to install one in accordance with local codes.

Most likely you connect blue to blue, and brown to red or brown.

BUT you should really test it with voltage and continuity tester to be 100% sure you're connecting outside thread of a bulb to neutral and the pin to live.

How I understand colours of your wiring at the ceiling:

1. green/yellow: ground
2. blue: neutral
3. red: circut 1 live
4. brown: circuit 2 live

I assumed you have 2 switches on the wall. If you have just one switch, then possibly one of the live wires is not connected at all OR the opposite: it's permanently connected (for remote-controlled lamps).

And wiring on the fixture:

1. blue: bulb thread (must be connected to neutral)
2. brown: bulb base (must be connected to live)
3. metal thingy - if your fixture has extra screw that's simply connected to the metal body of the lamp, this is where the yellow-green ground wire goes)

About the testing you should do: With a neon probe on the wires coming from the ceiling: turn both switches "on" and verify which wires are live. Turn the switches off (or even better, ask someone to keep cycling one of them) to verify if they switch off properly and which switch is which circuit. With a continuity tester (eg. ohmmeter or a buzzer) on a disconnected fixture: check if blue goes to thread and if brown goes to base. Sometimes you can disassemble the fixture a tiny bit to simply see where the wires go.