setSelectedTabIndicatorColorが非推奨になったので、addOnTabSelectedListenerを使用。
MainActivity.kt
        tab_layout.addOnTabSelectedListener(object : TabLayout.OnTabSelectedListener {
            override fun onTabReselected(p0: TabLayout.Tab?) {}
            override fun onTabUnselected(p0: TabLayout.Tab?) {}
            override fun onTabSelected(p0: TabLayout.Tab?) {
                tab_layout.setSelectedTabIndicatorColor(
                    ContextCompat.getColor(
                        applicationContext,
                        when (p0?.position) {
                            0 -> R.color.red
                            1 -> R.color.blue
                            else -> R.color.green
                        }
                    )
                )
            }
        })