A warm fire!
Actually I was pondering this recently. My house is colourful, with patterned rugs on wood floors, lots of paintings, plants, flowers in vases, some sculptures. The sofa is green velvet, the arm chair is a light mustard. But also it's got music or Radio 4 on, there are two dogs and two cats, the house looks lived in.
I have a friend who would always say that she couldn't believe how relaxed she was at my house. She'd come hang out for hours (she wasn't social at all). Her own house was pristine. She had a teen, a 22 year old and her partner living there but you'd think no one lived there. Nothing on the walls. Tasteful but dull furniture. No character. No books, no art, everything white or beige or brown. It was obviously her 'home' but it wasn't homely at all and even she could feel the difference. (By the way she wasn't dull - she was the school matron but on her off time was a Harley chick - tattoos and all)!