What should be done to balance the effect of deep warm colours in a narrow corridor?

Correct answer: Add areas of light cool colours

The governing concept is the spatial effect of colour temperature, value and contrast. Deep warm colours tend to advance and can make a narrow corridor feel smaller or more enclosed. Light cool colours tend to recede and reflect more light, helping the space appear wider and more open. Thus option B provides balance; adding red, black or orange would intensify the cramped effect.