Here's a start. I'm sure using one of the libraries you can adjust the Border colours.
B4X:
Sub Globals
'Declare the global variables here.
flag=0
End Sub
Sub App_Start
Form1.Show
button1.FontColor=cred
timer1.Enabled=true
End Sub
Sub Timer1_Tick
If flag=0 Then
button1.FontColor=cblue
flag=1
Return
End If
If flag=1 Then
button1.FontColor=cred
flag=0
Return
End If
End Sub
Small modification for developers who like short code:
B4X:
Sub Globals
'Declare the global variables here.
End Sub
Sub App_Start
Form1.Show
button1.FontColor=cred
timer1.Enabled=true
End Sub
Sub Timer1_Tick
If button1.FontColor = cRed then button1.FontColor = cBlue else button1.FontColor = cRed
End Sub