An interesting thing about human language is that color terms and variegation arose relatively late and are one of the more easily traced aspects of language for that reason. Thus, some languages have shades in common use which are not commonly used in others. Russian — ordinary street Russian — has two words for blue, not “light blue” and “dark blue” (which they are) but two completely different words (голубой, goluboy and синий, siniy). Meanwhile the Chinese word qing (青) is a color which is by nature changeable: it originally referred to the point in a flame or fire where the fire shifted from red into blue-and-green and thus 青 means both blue and green and connotes the idea of mutability.
This is one example of the fact that Chinese etymology can be traced back much further to roots and sources than Indo-European etymology goes. We don’t know why tree and three rhyme, but we do theorize that 木 and 目， which are sound-alikes are so called, perhaps, because to the ancients there were trees as far as the eyes could see. 相 and since tree and eye are sound alikes put them together as the symbol for “alike”/”similar”.
There are many other examples of words in Chinese where we know that figurative uses arose out of literal things. I don’t see that level of specificity in origins of Indo-European words. From Chinese etymology however we can and should hypothesize that sound-alikes are figurative extensions from literal uses of the same term. Thus it is a valid hypothesis that mutter and mother are related words in that only your mother would understand whatever you mutter, e.g.
The more I study Chinese the more I beleive in proto-world.