"Excitement is in the air" will be "Праздничная атмосфера". The second phrase is not proper English. You probably meant imperative "Lighten up" rather then declarative "To be lightened up". And you were not talking about colors in visual design, right? Even then it's too ambiguous. There is no one-to-one equivalent suitable for all cases. I'm sorry, I understand that this is not very useful answer, but it would be much easier to help you if you gave some context.

it is - Волнение в воздухе "." Стань Освети

it is - Волнение в воздухе "." Стань Освети

"Возбуждение в воздухе" - прямой перевод. Воспряни и Зажгись! Осветись! - может быть так сказать.

Lighten up - расслабся, не напрягайся. As for "excitement is in the air" - Cababunga gave the best translation.