Correct theming to black on green when in light theme.

app/src/main/java/com/geeksville/mesh/ui/theme/Color.kt

@@ -32,6 +32,8 @@ val LightPink = Color(0xFFFFE6E6)
 val LightGreen = Color(0xFFCFE8A9)
 val LightRed = Color(0xFFFFB3B3)
 
+val Black = Color(0x000000)
+
 val MeshtasticGreen = Color(0xFF67EA94)
 
 val HyperlinkBlue = Color(0xFF43C3B0)

app/src/main/java/com/geeksville/mesh/ui/theme/Theme.kt

@@ -22,6 +22,7 @@ import androidx.compose.material.MaterialTheme
 import androidx.compose.material.darkColors
 import androidx.compose.material.lightColors
 import androidx.compose.runtime.Composable
+import androidx.compose.ui.graphics.Color
 
 private val DarkColorPalette = darkColors(
     primary = MeshtasticGreen,
@@ -33,6 +34,7 @@ private val LightColorPalette = lightColors(
     primary = MeshtasticGreen,
     primaryVariant = LightSkyBlue,
     secondary = Teal200,
+    onPrimary = Color.Black
 
     /* Other default colors to override
     background = Color.White,