Don't worry about it. The Tamiya OD is fine. There are more opinions about the correct shade of OD as there are modelers. I often put a little German dark yellow, or "dunklegelb" as some like to call it, I prefer the English term, just to lighten it, but airbrush it randomly over the darker straight OD as part of my painting style.
I remember looking at some US tanks at a museum at Ft. Hood some time ago and noticing that the shade of OD would apparently change as I walked around them. This would seem to change from lighter to darker on the same side of the tank depending on my angle and the sun's, also if I was looking down on them, or if it was in shadow.
As far as I know there was no can of paint issued of "olive drab", the factories mixed it according to a ratio using a couple of colors. I'm sure I'll be corrected if I'm wrong, and I probably am.
If you wish, any weathering you do will change the look as well. Don't abandon hope with it just yet, and remember, it still may be accurate or close enough.
As a side note. My father spent WWII in the pacific on one ship, for 4 years and his only comment on the color of his ship was, "I don't know, grey I guess". BTW, it went though about 4 different "measures" or camouflage schemes during that time.
Doug