I'm buying a condo in a warehouse were old hard wood floors were sanded and sealed. A fair amount of the planks had to be replaced and the colors don't match. I don't expect them to be perfect, but the new floor is much lighter in color. Any suggestions? I'm fighting with the sellers aBOUT THIS.

Many times it is hard to match up new flooring to very old flooring. It may be that the flooring company used the wrong species of wood or the wrong grade. If it is douglas fir (a wood often used in wharehouses), it gets dark with age and that can't be duplicated. Maybe all that can be done is resand the floors and stain them so they will all have the same color stain. This will work only IF the correct species of wood was used. If not, you can either try to get them to correct the problem OR look for another property.

If the sealer they used is an oil-based sealer made for wood floors, a coat of finish that has been tinted can be applied to the new wood to tone it down to look like the old wood. You may need two coats on the new wood if there is a big color difference. Do a small test area to see if you get the color you want. We use two buckets of finish and two brushes,one with the tint for the new wood and the other without the tinting for the old wood and coat the areas at the same time if the floor has been laced in. If you get the color to what you want then final coat the entire floor with the untinted finish.
If the floor has to be resanded I would use oil-based sealer only on the old wood so it will get to the color it is going to be when finished then try to match the color on the new wood with stain. If you sand the entire floor then stain the whole floor, the old wood will still be darker than the new wood almost every time.
If the floor finisher is a pro he should know how to make the floor look good.
Buddy