Color can be confusing. If you have mastered the meaning of ‘tone’ (light to dark) then you must now continue to use light tones and dark tones of many colors in the painting.
Try to think of it this way – you wish to paint scenes with foreground things, say a barn and background things, say mountains. Between you, the barn and the mountains is air. The air is transparent 99% but 1% is blue. So the further away things are the more air is between you and it and the bluer the thing will look. But it will look pale blue, not dark blue. That is why we must not use black in a landscape painting. You can not see the color black when it moves away from you, it absorbs the blue of the air or red of the sunset or green reflected light from the local trees and it is not black any more. We can not add white to the black as it is still a tone of black, not natural. Natural colors are always a combination of the colors of the day which vary from morning to night. So do not just pick any color that looks pretty to put in your mountains, that mountain color should run right through your painting, it should be in the grey under your feet and in the grey of the clouds above you. So technically you should be able to paint a picture using only one of each color, red, blue, yellow and white.
The different paint manufacturers and types of paint and qualities of paint make it impossible for me to tell you exactly how to mix colors and tones of colors. Be careful not to add yellow to blue, add the littlest bit of blue to yellow to get your greens. Adding yellow to blue will leave you with a huge amount of dark green paint. Add crimson slowly to blue as crimson can be very strong. All in all take your time and experiment and learn.