What are hair levels and how they impact hair color?
Levels are the degree of "lightness or darkness" of a color that is "reflected or seen" by the eye. Hair color is assigned a Level 'number' from 1 to 10 with 1 being black and 10 lightest blonde. In other words, black reflects very little light and lightest blonde reflects the greatest amount of light. A level 10 blonde would be 'two steps lighter' than a level 8 blonde. This system of levels applies to all colors and almost all hair color brands commonly found.

What are tones and how they balance the underlying exposed pigment?
Tone refers to whether a hair color is warm or cool. The warm (golden) colors are red, orange and yellow. You may have noticed on some hair color boxes, there are references to "medium warm brown" or "natural golden blonde". This means the undertone of the color is warm - either red, orange, or yellow. These can be used to give hair a warmer look. The cool (ash) colors are blue, green, and violet/purple (same thing). When the hair color names refer to "dark ash blonde" and so forth, it means they have a green, blue, or purple undertone. These you should be careful with. If you put a green or blue undertone hair color on a warm color (especially a gold/yellow color) hair, you will come out with green.
• Cool: Add cool tones while minimizing red, gold, or brassiness.
• Neutral: Balance cool and warm tones; keeps hair closest to your current tone.
• Warm gold, caramel and bronze: These colors add golden highlights and tones.
• Warm red and warm brown: These colors add red highlights and tones.