Coordinating floor colour with wall colour is the basis for a good design theme. A two-tone floor design tends to suggest the wall colours for the room. However, if these colours will not do, look to inspiration from nature, as blue and grey crop up in many natural scenic locations.
As grey is one of the neutral colours, consider adding another neutral colour to the wall. Neutrals tend to pair well with most colours, creating a soothing environment. Pairing a grey and blue floor with an ivory or cream wall brightens the room up and grounds it by emphasising the floor. A soft lighter grey wall gives a cosy feel to the room while a darker pewter grey, almost black tinged, brings a dramatic appeal.
Blue comes in a range of shades, creating a multitude of effects. Using a blue similar to the floor tile brings the eye up from the floor to the ceiling creating an illusion of a taller room, while using a darker or lighter shade of the floor blue gives you a muted appearance. Another option combines different blues for a contrasting, dramatic appearance. For example, a deep midnight blue, navy blue or indigo blue floor grounds a light pastel blue or powder blue wall.
Nature gives several examples of colours that combine with blue and grey. Bring in a forest green, moss green or a sage green wall to suggest the grasses and trees that surround grey river rocks and streams found in forests or coastal cliffs. The metallic gold found in river rocks can be incorporated onto your walls by painting them a bright yellow and adding a faux treatment to create a golden sheen.
Combining the two floor colours of blue and grey into a pattern gives continuity to the room design. A two-tone paint treatment on the walls -- one floor colour on top with the other on the bottom separated by a chair rail -- gives a designer look to the room. Large horizontal railroad stripes gives visual appeal. Paint vertical stripes solely on the top portion of the wall, with the bottom a solid grey or blue.