stock HealthToColor(Float:Health)  
{  
     new Color;  
     if(Health <= 100 && Health >= 50)Color = ( (floatround(255 - (Health * 5.1))) << 24 | 255 << 16 | 0 << 8 | 255 << 0);  
     if(Health <= 50 && Health >= 0)Color = (255 << 24 | (floatround(Health * 5.1)) << 16 | 0 << 8 | 255 << 0);  
     return Color;  
}

public OnPlayerUpdate(playerid)  
{  
     new Float:Health,string[12];  
     GetPlayerHealth(playerid,Health);  
     format(string,sizeof(string),"%.f HP",Health);  
     SetPlayerChatBubble(playerid,string,HealthToColor(Health),20.0,1500);  
     return true;  
}