Old built-in shelves, especially dark or heavily varnished ones, can dominate a room. They cut the wall into heavy blocks and draw the eye to themselves instead of to what’s on them.
Painting them the same colour as the wall helps them recede. The overall effect is calmer and more streamlined, because your eye reads it as a single surface with interesting items on it, not “big brown unit stuck on white wall.”
This trick is particularly useful in smaller rooms or narrow spaces where big pieces can make things feel crowded. By unifying colour, you keep the function of storage but reduce the sense of bulk.
You can still style shelves with colour and texture through books, plants and decor, but the structure itself stops shouting for attention.