Could it be that they don't match, because you've painted them many times over previous coats?
Remember, acrylic paints (and especially airbrush ones) are translucent. So, if you paint light tan over black, it will look different from light tan over green. To cover a dramatically different color and achieve opacity, you're often looking at a dozen coats on those light colors.
One way that you can get them closer together in color is to mask out all the non-light brown parts , airbrush an acceptable wash, lightly thinned (like Agrax or Seraphim serra), let it fully dry, then airbrush it again with a light coat of the same color (the light brown that you used).
Because the light brown is really quite light, a GENTLE airbrushed wash will tint it all enough that a further coat should even the colors out.
The other thing you can do is to apply some washes, poaint out some details (like the ornate edges of the shoulders) and apply some weathering. Once you do that, somewhat different shades of a color tend to be a lot less noticeable.
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