Purple seedliings

I don't have a picture at the moment and will snap one this afternoon....

Yesterday I noticed a bunch of my seedlings with a purple color on the stem and undersides of the leaves.  My tomatoes have it the worst but noticed a bit on a few other plants.  I have these tomatoes growing under a 300W LED light and growing in a mix of 1/2 Coast of Maine potting mix, 1/4 coconut coir, 1/4 earthworm castings.  Other plants growing outside of my 300w LED (either window light or a Feit LED grow light that is white) do not have this purple color.  I feel like the light might be causing this...

My 300w LED is intensely pink.

Apologies for asking a super obvious question but have you examined the purple ones under the other lights?  I have two lights myself, one that looks white to the eye and one that is pot purple pink.  The ones under the purple light look bizarre (purple stems, brown grey leaves, etc) but move them to the other light or outside and look completely normal.

Nikko wrote:I don't have a picture at the moment and will snap one this afternoon....

Yesterday I noticed a bunch of my seedlings with a purple color on the stem and undersides of the leaves.  My tomatoes have it the worst but noticed a bit on a few other plants.  I have these tomatoes growing under a 300W LED light and growing in a mix of 1/2 Coast of Maine potting mix, 1/4 coconut coir, 1/4 earthworm castings.  Other plants growing outside of my 300w LED (either window light or a Feit LED grow light that is white) do not have this purple color.  I feel like the light might be causing this...

My 300w LED is intensely pink.

I don't know anything about lights as I use a window but my tomatoes get purple under the leaves when they get cold.

BUT...I just found this:
Phosphorus Deficiency
Tomatoes suffering from phosphorus deficiency exhibit symptoms such leaves showing purple veins or with an overall purple color. Other symptoms include a bronze coloring of leaves and a red color along vein margins. Managing this problem requires adding phosphorus to the soil. This is done by adding bone meal to the soil or using Epsom salt (the magnesium helps soak up the phosphorus) as a foliar spray.
http://homeguides.sfgate.com/causes-tomato-plants-purple-41716.html

Another one:
Why Are Plant Leaves Turning Purple? When you notice a plant with purple leaves rather than the normal green color, it is most likely due to a phosphorus deficiency. All plants need phosphorus (P) in order to create energy, sugars and nucleic acids. Young plants are more likely to display signs of phosphorus deficiency than older plants. If the soil is cool early in the growing season, a phosphorus deficiency may develop in some plants. The underside of marigold and tomato plant leaves will turn purple with too little phosphorus while other plants will be stunted or turn a dull dark-green color.
https://www.gardeningknowhow.com/plant-problems/environmental/leaves-turning-reddish-purple.htm

CC

I planted my purple-leafed tomatoes a few days ago and the new leaves are green. Your should turn green when they are planted in Mel's Mix.