我是Jetpack作曲的新手。我是按照教程和问题是，根据教程的文本颜色是黑色的预览以及在真实的的设备（在教程）

在我的预览中，我也看到颜色是黑色的，然而，当我在我的两个不同的设备上运行应用程序时，我看到颜色是白色的。
我错过了什么？

UPD

package com.example.composableexmp

import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.foundation.background
import androidx.compose.foundation.layout.*
import androidx.compose.foundation.shape.CornerSize
import androidx.compose.foundation.shape.RoundedCornerShape
import androidx.compose.material.MaterialTheme
import androidx.compose.material.Surface
import androidx.compose.material.Text
import androidx.compose.runtime.Composable
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.clip
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.text.font.FontWeight
import androidx.compose.ui.tooling.preview.Preview
import androidx.compose.ui.unit.dp
import com.example.composableexmp.ui.theme.ComposableExmpTheme

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            MyApp {
                TopHeader()
            }
        }
    }
}

@Composable
fun MyApp(content: @Composable () -> Unit) {
    ComposableExmpTheme {
        Surface(
            color = MaterialTheme.colors.background
        ) {
            content()
        }
    }
}

@Preview
@Composable
fun TopHeader(totalPerPerson: Double = 0.0) {
    Surface(
        modifier = Modifier
            .fillMaxWidth()
            .height(150.dp)
            .clip(shape = RoundedCornerShape(corner = CornerSize(12.dp))),
        color = Color(color = 0xFFE9D7F7)
    ) {
        Column(
            modifier = Modifier.padding(12.dp),
            horizontalAlignment = Alignment.CenterHorizontally,
            verticalArrangement = Arrangement.Center
        ) {
             val total = "%.2f".format(totalPerPerson)

            Text(
                text = "Total Per Person",
                style = MaterialTheme.typography.h5
            )

            Text(
                text = "$$total",
                style = MaterialTheme.typography.h4,
                fontWeight = FontWeight.ExtraBold
            )
        }
    }
}

@Preview(showBackground = true)
@Composable
fun DefaultPreview() {
    ComposableExmpTheme {
        MyApp {
            Text(text = "Hello Again")
        }
    }
}