There are multiple instances in the Book of Mormon where the fruit of the tree of life is referred to as being “white” or “light”. For example in 1 Nephi 8:11
And it came to pass that I did go forth and partake of the fruit thereof; and I beheld that it was most sweet, above all that I ever before tasted. Yea, and I beheld that the fruit thereof was white, to exceed all the whiteness that I had ever seen.
Similarly, Alma speaks of eating the seed which is “light” in Alma 32:35, 42
O then, is not this real? I say unto you, Yea, because it is light; and whatsoever is light, is good, because it is discernible, therefore ye must know that it is good; and now behold, after ye have tasted this light is your knowledge perfect?
And because of your diligence and your faith and your patience with the word in nourishing it, that it may take root in you, behold, by and by ye shall pluck the fruit thereof, which is most precious, which is sweet above all that is sweet, and which is white above all that is white, yea, and pure above all that is pure; and ye shall feast upon this fruit even until ye are filled, that ye hunger not, neither shall ye thirst.
This is interesting because the association between the tree of life and the white/light fruit is anciently attested. Zofja Ameisenowa and W. F. Mainland comment that:
It must be noted that in almost all mythologies the Tree of Life is associated with light because the whole of organic life is dependent upon the light of the sun.– Zofja Ameisenowa and W. F. Mainland, “The Tree of Life in Jewish Iconography,” Journal of the Warburg Institute 2, no. 4 (1939), 335.
If Joseph Smith had made up the story of the tree of life, why would he say the fruit was white?