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When scanning a 35mm film, if I let Epson's software doing its thing by choosing the "color negative film" mode, without any other adjustment, the resulting raw scan will be yellowish. However, if I do the other method by scanning in positive(orange) film and then invert the curve in the post in photoshop, the resulting scan will be tealish. Why is the difference?

Scanning handles removing the overall orange mask in color negative film.

Scanning as positive, and then postprocessing invert does not remove it, inversion simply turns that orange mask to a deep blue overall. NOT Bluish, but very strongly deep blue. Then additional work to try to remove it.

This is a difficult job to do in digital postprocessing (not meaning the process but the result), because such extreme color shifts (to remove the strong blue) strongly risks clipping in digital. Clipping can somewhat change the colors and can lose detail.

Whereas the scanner can do this as analog (no digital clipping) by simply varying the scan time duration for each of the RGB colors (result acting like a corrective filter in the light). Scanning color negatives is a bit slower than positive slides, but it is a very good thing.

Not saying it is "impossible" in digital, you might achieve an acceptable result, but it is just really not the same. If you have the scanner, I strongly suggest using it. It is designed for the exact purpose.

That is speaking of color negatives, they are the special problem. Positive slides or prints or B&W negatives don't have the orange mask, so then other copy methods than scanning are not ruled out (but scanners are still good too).

The result of a yellowish cast is not inherent at all. But it will be tremendously easier to manage than the deep blue otherwise. :) There are various factors however.

Not every brand of color negative film has the same exact color of orange mask, so some scanners offered a menu of film choices.
Or the scanner calibration might not be exact.

Or more commonly likely, the film might just have been shot with an incorrect color white balance (we had very little choice with film, but there was a base choice of film type or flash bulb type or lighting or filters). Often the shot needed better white balance correction itself. So try scanning other different film negatives in their different lighting situations to see how constant the yellowish cast is? Sunshine outdoors is likely more accurate than indoors.

In digital work, it would have been better if the digital camera white balance had been correct, but usually, it might be fairly mild and easily corrected in postprocessing.

White balance was the same problem for film as digital is today, however the lab printing the picture from film did a good job back then correcting it for us. But it is NOT yet corrected in the negative itself.

Remember the blue flashbulbs? Remember that we still got a good result whether we used them or not? The printing lab fixed it for us. But in digital, or in film scans, that is now our job to correct.