(Note: I'm in Canada, so standards may be different.) For a CEO position, I'd err on the side of more formal. Suit jacket (blazer) and a matching bottom, either a pencil skirt or slacks. Colour would depend on the company/industry. If it's a more casual or creative company, you could do a bright colour, with a white blouse underneath. If it's a conservative industry you might want black, grey, or navy, with either a white or coloured (solid or patterned) blouse. Lykke til!