Hi CT,
Regarding Watco... It isn't uncommon to have slight color differences from batch to batch. This is true of any stain or finish. There is always inconsistency. The best bet is to always buy more than you need for a project. This way you have a consistent finish, provided you stirred well.
Compare the lot or batch numbers on the can. You are looking for them to match.
The green poplar thing has a remedy, but you have to like the remedy...
Here is a place where you can look at swatches of Watco colors.
http://www.watco.net/CBGProduct.asp?pid=46Another strategy, if you have similar products from different batch lots, no matter. Get a clean bucket, pour them into it and mix, then pour them back into their cans and you will have normalized the batches. now they are a new batch.
Cool thing is about Watco, the base is the same, so if you want your own color, mix 2 together. Just keep track of your ratios. Mix something you like better than Poplar green and see if you can make it better. I have worked with quite a bit of poplar and Watco Medium Walnut. The green went away.
My need was for a dark wood though, and that may not be what you want, but then you may be willing to do a number of things... To be rid of the Poplar curse!

A 60-1/2 or or LV LA block can be fitted with a higher angle grind on the blade to aid in planing a raised panel. Final pitch angles while bedded is up to you, the block come with a 12 degree bed. The standard LA blade grind is 25*. The grind you choose is all you. Veritas supplies with 38* LA, 50* York, and 62* half pitch for all their LA planes and the same grinds are just as easy to use with other block planes. Then it is just a matter of working to your layout marks.
In all it really just makes any adjustable mouth block plane into a swiss army knife... Food for thought.
Good luck, HTH