Blending occurs everywhere on paintings, not just backgrounds. I lay a white base down every time. It seems to give me more time, the blend is softer and more manageable. The brush strokes follow the direction of the form, great for shading and creating realistic effects.
Working from the top, apply paint wet on wet with the confidence that you will complete the blending before the paint begins to dry. If you are a little nervous about blending a large area because the paint might dry out before you finish, add a little puddle of ‘Hot weather thinners’ to the palette to slow up the drying time. Pick some up with a brush full of paint as you go along. There are other products you can get from the art supplies that slow down the drying. Be well organised, set up ready to go. Colours, extender on the palate, wet brushes, clearance around the board, water troughs, working area masked so you can concentrate on the blend. Masking is not naughty. Mask off your area so you can use bigger brushes for blends and special effects are possible.
As for getting the colours right you can refer to the colour wheel, rely on your experience or just take a chance. If you are not happy with the colours you simply let the paint dry and go again. If you want strong colours add more as you go back over the blend but keep the whole effect wet. It’s easier and the paint appears richer with the initial blend sitting under it. Finish with a clean dry brush to softly blend to a smooth transition between colours.