Thanks for the comments guys,
As for the sky, truth be told I've done no PP on the 2 shots you mentioned aurele, those 2 were taken at around 10pm just after the sunset, blue hour I think it is called, a very short period of time when the sky was indeed in this stunning colour. I was lucky to have this 2 days in a roll :P I love the way when view from above Arc de Triumph at this period time the whole city was blanketted by this mystic light, Paris is truely beautiful at night!
Check the link below for the explaination of it from wikipedia.
Blue hour - Wikipedia, the free encyclopedia
And I have to agree the Arc de Triumph was indeed enormous!