White will lighten and heighten the ceiling as Vagrant and Lucca say, especially where there are any shadows caused by the beams. But if you want to keep a 'period charm' look you might consider an 'aged white' appearance, using a darker creamish sort of colour. (Think of old country pub ceilings).This could sit well alongside the grey, too, without being too dark in itself. Apart from when white alone is used, ceilings are almost never painted the same colour as walls - it tends to shrink the room.