Thanks for your inquiry.
Different elisa kits might have different curves.Let us see the examples of kits which employes sanwitch method and competition method.They both have OD values as X-axis and the concentraction of antigen as Y-axis.
For kits of sanwitch method,the concentration of antigen is directly proportional to the OD value.In the detection range of the kit,OD values increase when concentration of antigen increases。For the kits of competition method,you can refer to the manual of the kits.In the dtection range of the kit,the OD values decrease with increase of antigen concentration.Thus the pics on the web is normal and with no problems.Regarding the mentioned kit#CSB-E13210G,Goat Haptoglobin,Hpt/HP ELISA KIT, competitive inhibition enzyme immunoassay technique is employeed.The OD value of samples is inversely proportional to the concentration.It developes deeper color,it will have higher OD value and lower concentration. Pls let me know if you have any further questions. Thank you.

The dilution factor 1:500 is a recommanded diltuion factor.We suggest you use it as a baseline and do the pre-testing first and confirm the best dilution factor for your own test.Usually the dilution factor you will obtain from the pre-testing is usually not too far away from the recommanded diltuion factor.We are sorry the the specific information of the sample diluent is confidential and we are not able to disclosed it.
May I know why you need 1:50000?What results do you need to get by 1:50000?
No colour means max concentration of 1000ng/ml..isnt it?---As to this question about the color,we could not inform you a general conclustion.It needs to be based on specific situation.For example,how is the "no color" caused?