New ceiling light with 2 cables, both same

Hi I know the type of clear flex you mean and there are no colour markings on like you say. The light will work whichever way you connect it up. Technically if lamp holders are screw type then the live wire should be the one that goes to the back pin of the lamp holder & the neutral to side clamps but you will need a continuity tester to bell that out. If it has a bayonet type lamp holder then it really doesn't matter which way they go round as both pins are identical. Yes that does mean double insulated & no earth required. With regards to house earth it just needs to be put into some sort of connector block if more than 1 earth then join them all together in the same block.

This is a double insulated fitting as you quite rightly say with the symbol inside the fitting. Hence the clear cables, the earth cable(s) on the wiring just need a connector on and left inside the fitting. The clear cables can be connected either way. If in any doubt consult an electrician.